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Papers by Amy Luke

Research paper thumbnail of Meta-Analysis of Genome-Wide Linkage Studies in Celiac Disease

Research paper thumbnail of Daily activity patterns of 2316 men and women from five countries differing in socioeconomic development

Chronobiology International, 2015

Daily rhythmicity in the locomotor activity of laboratory animals has been studied in great detai... more Daily rhythmicity in the locomotor activity of laboratory animals has been studied in great detail for many decades, but the daily pattern of locomotor activity has not received as much attention in humans. We collected waist-worn accelerometer data from more than 2000 individuals from five countries differing in socioeconomic development and conducted a detailed analysis of human locomotor activity. Body mass index (BMI) was computed from height and weight. Individual activity records lasting 7 days were subjected to cosinor analysis to determine the parameters of the daily activity rhythm: mesor (mean level), amplitude (half the range of excursion), acrophase (time of the peak) and robustness (rhythm strength). The activity records of all individual participants exhibited statistically significant 24-h rhythmicity, with activity increasing noticeably a few hours after sunrise and dropping off around the time of sunset, with a peak at 1:42 pm on average. The acrophase of the daily rhythm was comparable in men and women in each country but varied by as much as 3 h from country to country. Quantification of the socioeconomic stages of the five countries yielded suggestive evidence that more developed countries have more obese residents, who are less active, and who are active later in the day than residents from less developed countries. These results provide a detailed characterization of the daily activity pattern of individual human beings and reveal similarities and differences among people from five countries differing in socioeconomic development. 650 Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only.

Research paper thumbnail of 25-hydroxyvitamin D levels in African American and Nigerian women

American Journal of Human Biology, 2013

Americans have substantially lower levels of circulating 25(OH)D than whites. We compared populat... more Americans have substantially lower levels of circulating 25(OH)D than whites. We compared population-based samples of 25(OH)D in women of African descent from Nigeria and metropolitan Chicago.

Research paper thumbnail of The long isoform uncoupling protein-3 (UCP3L) in human energy homeostasis

International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity, 1999

The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon ami... more The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon amino acid sequence homology to UCP1. Spontaneous mutations of UCP3> have been described in humans, but not in rodents. The functional consequences-or lack thereof-of these mutations in humans will be of great importance in elucidating the biology of this protein. The results of two such studies are summarized here.

Research paper thumbnail of A genome-wide linkage analysis investigating the determinants of blood pressure in whites and African Americans

American journal of hypertension, 2003

Evidence for genomic regions influencing systolic and diastolic blood pressure (BP) were assessed... more Evidence for genomic regions influencing systolic and diastolic blood pressure (BP) were assessed in a whole genome linkage analysis in 211 African American and 160 white families as part of the GenNet network of the National Heart, Lung and Blood Institute-sponsored Family Blood Pressure Program. Multipoint regression and variance components linkage methods were used to analyze 372 polymorphic markers. Statistically compelling evidence for linkage (P values .0057 and .00023, respectively) was found on chromosome 1. Our results support the idea that BP regulation is most likely governed by multiple genetic loci, each with a relatively weak effect on BP in the population at large.

Research paper thumbnail of Linkage disequilibrium and haplotype diversity in the genes of the renin-angiotensin system: findings from the family blood pressure program

Genome research, 2003

Association studies of candidate genes with complex traits have generally used one or a few singl... more Association studies of candidate genes with complex traits have generally used one or a few single nucleotide polymorphisms (SNPs), although variation in the extent of linkage disequilibrium (LD) within genes markedly influences the sensitivity and precision of association studies. The extent of LD and the underlying haplotype structure for most candidate genes are still unavailable. We sampled 193 blacks (African-Americans) and 160 whites (European-Americans) and estimated the intragenic LD and the haplotype structure in four genes of the renin-angiotensin system. We genotyped 25 SNPs, with all but one of the pairs spaced between 1 and 20 kb, thus providing resolution at small scale. The pattern of LD within a gene was very heterogeneous. Using a robust method to define haplotype blocks, blocks of limited haplotype diversity were identified at each locus; between these blocks, LD was lost owing to the history of recombination events. As anticipated, there was less LD among blacks, ...

Research paper thumbnail of An international comparative study of blood pressure in populations of European vs. African descent

BMC medicine, 2005

The consistent finding of higher prevalence of hypertension in US blacks compared to whites has l... more The consistent finding of higher prevalence of hypertension in US blacks compared to whites has led to speculation that African-origin populations are particularly susceptible to this condition. Large surveys now provide new information on this issue. Using a standardized analysis strategy we examined prevalence estimates for 8 white and 3 black populations (N = 85,000 participants). The range in hypertension prevalence was from 27 to 55% for whites and 14 to 44% for blacks. These data demonstrate that not only is there a wide variation in hypertension prevalence among both racial groups, the rates among blacks are not unusually high when viewed internationally. These data suggest that the impact of environmental factors among both populations may have been under-appreciated.

Research paper thumbnail of Comparisons of intensity-duration patterns of physical activity in the US, Jamaica and 3 African countries

BMC Public Health, 2014

Background: This difference in how populations living in low-, middle or upper-income countries a... more Background: This difference in how populations living in low-, middle or upper-income countries accumulate daily PA, i.e. patterns and intensity, is an important part in addressing the global PA movement. We sought to characterize objective PA in 2,500 participants spanning the epidemiologic transition. The Modeling the Epidemiologic Transition Study (METS) is a longitudinal study, in 5 countries. METS seeks to define the association between physical activity (PA), obesity and CVD risk in populations of African origin: Ghana (GH), South Africa (SA), Seychelles (SEY), Jamaica (JA) and the US (suburban Chicago). Methods: Baseline measurements of objective PA, SES, anthropometrics and body composition, were completed on 2,500 men and women, aged 25-45 years. Moderate and vigorous PA (MVPA, min/d) on week and weekend days was explored ecologically, by adiposity status and manual labor. Results: Among the men, obesity prevalence reflected the level of economic transition and was lowest in GH (1.7%) and SA (4.8%) and highest in the US (41%). SA (55%) and US (65%) women had the highest levels of obesity, compared to only 16% in GH. More men and women in developing countries engaged in manual labor and this was reflected by an almost doubling of measured MPVA among the men in GH (45 min/d) and SA (47 min/d) compared to only 28 min/d in the US. Women in GH (25 min/d), SA (21 min/d), JA (20 min/d) and SEY (20 min/d) accumulated significantly more MPVA than women in the US (14 min/d), yet this difference was not reflected by differences in BMI between SA, JA, SEY and US. Moderate PA constituted the bulk of the PA, with no study populations except SA men accumulating > 5 min/d of vigorous PA. Among the women, no sites accumulated >2 min/d of vigorous PA. Overweight/obese men were 22% less likely to engage in manual occupations. Conclusion: While there is some association for PA with obesity, this relationship is inconsistent across the epidemiologic transition and suggests that PA policy recommendations should be tailored for each environment.

Research paper thumbnail of Distribution of metals exposure and associations with cardiometabolic risk factors in the “Modeling the Epidemiologic Transition Study”

Environmental Health, 2014

Background: The vitamin D-endocrine system is thought to play a role in physiologic processes tha... more Background: The vitamin D-endocrine system is thought to play a role in physiologic processes that range from mineral metabolism to immune function. Serum 25-hydroxyvitamin D [25(OH)D] is the accepted biomarker for vitamin D status. Skin color is a key determinant of circulating 25(OH)D concentrations, and genes responsible for melanin content have been shown to be under strong evolutionary selection in populations living in temperate zones. Little is known about the effect of latitude on mean concentrations of 25(OH)D in dark-skinned populations. Objective: The objective was to describe the distribution of 25(OH)D and its subcomponents in 5 population samples of African origin from the United States, Jamaica, Ghana, South Africa, and the Seychelles. Design: Participants were drawn from the Modeling of the Epidemiologic Transition Study, a cross-sectional observational study in 2500 adults, ages 25-45 y, enrolled between January 2010 and December 2011. Five hundred participants, w50% of whom were female, were enrolled in each of 5 study sites: Chicago, IL (latitude: 418N); Kingston, Jamaica (178N); Kumasi, Ghana (68N); Victoria, Seychelles (48S); and Cape Town, South Africa (348S). All participants had an ancestry primarily of African origin; participants from the Seychelles trace their history to East Africa. Results: A negative correlation between 25(OH)D and distance from the equator was observed across population samples. The frequency distribution of 25(OH)D in Ghana was almost perfectly normal (Gaussian), with progressively lower means and increasing skewness observed at higher latitudes. Conclusions: It is widely assumed that lighter skin color in populations outside the tropics resulted from positive selection, driven in part by the relation between sun exposure, skin melanin content, and 25(OH)D production. Our findings show that robust compensatory mechanisms exist that create tolerance for wide variation in circulating concentrations of 25(OH)D across populations, suggesting a more complex evolutionary relation between skin color and the vitamin D pathway. This trial was registered at clinicaltrials.gov as NCT02111902.

Research paper thumbnail of 25-Hydroxyvitamin D in African-origin populations at varying latitudes challenges the construct of a physiologic norm

American Journal of Clinical Nutrition, 2014

Background: The vitamin D-endocrine system is thought to play a role in physiologic processes tha... more Background: The vitamin D-endocrine system is thought to play a role in physiologic processes that range from mineral metabolism to immune function. Serum 25-hydroxyvitamin D [25(OH)D] is the accepted biomarker for vitamin D status. Skin color is a key determinant of circulating 25(OH)D concentrations, and genes responsible for melanin content have been shown to be under strong evolutionary selection in populations living in temperate zones. Little is known about the effect of latitude on mean concentrations of 25(OH)D in dark-skinned populations. Objective: The objective was to describe the distribution of 25(OH)D and its subcomponents in 5 population samples of African origin from the United States, Jamaica, Ghana, South Africa, and the Seychelles. Design: Participants were drawn from the Modeling of the Epidemiologic Transition Study, a cross-sectional observational study in 2500 adults, ages 25-45 y, enrolled between January 2010 and December 2011. Five hundred participants, w50% of whom were female, were enrolled in each of 5 study sites: Chicago, IL (latitude: 418N); Kingston, Jamaica (178N); Kumasi, Ghana (68N); Victoria, Seychelles (48S); and Cape Town, South Africa (348S). All participants had an ancestry primarily of African origin; participants from the Seychelles trace their history to East Africa. Results: A negative correlation between 25(OH)D and distance from the equator was observed across population samples. The frequency distribution of 25(OH)D in Ghana was almost perfectly normal (Gaussian), with progressively lower means and increasing skewness observed at higher latitudes. Conclusions: It is widely assumed that lighter skin color in populations outside the tropics resulted from positive selection, driven in part by the relation between sun exposure, skin melanin content, and 25(OH)D production. Our findings show that robust compensatory mechanisms exist that create tolerance for wide variation in circulating concentrations of 25(OH)D across populations, suggesting a more complex evolutionary relation between skin color and the vitamin D pathway. This trial was registered at clinicaltrials.gov as NCT02111902.

Research paper thumbnail of Association between smoking and total energy expenditure in a multi-country study

Nutrition & Metabolism, 2014

Background: The association between smoking and total energy expenditure (TEE) is still controver... more Background: The association between smoking and total energy expenditure (TEE) is still controversial. We examined this association in a multi-country study where TEE was measured in a subset of participants by the doubly labeled water (DLW) method, the gold standard for this measurement. Methods: This study includes 236 participants from five different African origin populations who underwent DLW measurements and had complete data on the main covariates of interest. Self-reported smoking status was categorized as either light (<7 cig/day) or high (≥7 cig/day). Lean body mass was assessed by deuterium dilution and physical activity (PA) by accelerometry.

Research paper thumbnail of Under-reporting of dietary energy intake in five populations of the African diaspora

British Journal of Nutrition, 2015

Studies on the role of diet in the development of chronic diseases often rely on self-report surv... more Studies on the role of diet in the development of chronic diseases often rely on self-report surveys of dietary intake. Unfortunately, many validity studies have demonstrated that self-reported dietary intake is subject to systematic under-reporting, although the vast majority of such studies have been conducted in industrialised countries. The aim of the present study was to investigate whether or not systematic reporting error exists among the individuals of African ancestry (n 324) in five countries distributed across the Human Development Index (HDI) scale, a UN statistic devised to rank countries on non-income factors plus economic indicators. Using two 24 h dietary recalls to assess energy intake and the doubly labelled water method to assess total energy expenditure, we calculated the difference between these two values ((self-report 2 expenditure/expenditure) £ 100) to identify under-reporting of habitual energy intake in selected communities in Ghana, South Africa, Seychelles, Jamaica and the USA. Under-reporting of habitual energy intake was observed in all the five countries. The South African cohort exhibited the highest mean under-reporting (252·1 % of energy) compared with the cohorts of Ghana (222·5 %), Jamaica (2 17·9 %), Seychelles (2 25·0 %) and the USA (2 18·5 %). BMI was the most consistent predictor of underreporting compared with other predictors. In conclusion, there is substantial under-reporting of dietary energy intake in populations across the whole range of the HDI, and this systematic reporting error increases according to the BMI of an individual.

Research paper thumbnail of Physical activity and pre-diabetes—an unacknowledged mid-life crisis: findings from NHANES 2003–2006

PeerJ, 2014

The prevalence of pre-diabetes (PD) among US adults has increased substantially over the past two... more The prevalence of pre-diabetes (PD) among US adults has increased substantially over the past two decades. By current estimates, over 34% of US adults fall in the PD category, 84% of whom meet the American Diabetes Association's criteria for impaired fasting glucose (IFG). Low physical activity (PA) and/or sedentary behavior are key drivers of hyperglycemia. We examined the relationship between PD and objectively measured PA in NHANES 2003-2006 individuals between 20 and 65 yrs.We excluded all participants without IFG measures or adequate accelerometry data (final N = 1,317). Participants were identified as PD if FPG was 100-125 mg/dL (5.6-6.9 mmol/L). Moderate and vigorous PA in minutes/day individuals were summed to create the exposure variable "moderate-vigorous PA" (MVPA). The analysis sample included 884 normoglycemic persons and 433 with PD. There were significantly fewer PD subjects in the middle (30.3%) and highest (24.6%) tertiles of PA compared to the lowest tertile (35.5%). After adjusting for BMI, participants were 0.77 times as likely to be PD if they were in the highest tertile compared to the lowest PA tertile (p < 0.001). However, these results were no longer significant when age and BMI were held constant. Univariate analysis revealed that physical activity was associated with decreased fasting glucose of 0.5 mg/dL per minute of MVPA, but multivariate analysis adjusting for age and BMI was not significant. Overall, our data suggest a negative association between measures of PA and the prevalence of PD in middle-aged US adults independent of adiposity, but with significant confounding influence from measures of BMI and age. Assah FK, Brage S, Ekelund U, Wareham NJ. 2008. The association of intensity and overall level of physical activity energy expenditure with a marker of insulin resistance. Diabetologia 51(8):. Dela F, Mikines KJ, Von Linstow M, Secher NH, Galbo H. 1992. Effect of training on insulin-mediated glucose uptake in human muscle. A, Coen P, Goodpaster BH. 2011. Effects of weight loss and exercise on insulin resistance, and intramyocellular triacylglycerol, diacylglycerol and ceramide. Diabetologia 54(5):Pharmacological and lifestyle interventions to prevent or delay type 2 diabetes in people with impaired glucose tolerance: systematic review and meta-analysis. BMJ 334(7588):299-307 Helmerhorst HJ, Wijndaele K, Brage S, Wareham NJ, Ekelund U. 2009. Objectively measured sedentary time may predict insulin resistance independent of moderate-and vigorous-intensity physical activity. Diabetes 58(8):. 2008. Efficacy of a theory-based behavioural intervention to increase physical activity in an at-risk group in primary care (ProActive UK): a randomised trial. Lancet 371(9606):41-48

Research paper thumbnail of Hepatitis C in sub-saharan Africa: urgent need for attention

Open forum infectious diseases, 2014

The hepatitis C virus (HCV), which was not recognized as an infectious agent until the 1980s, is ... more The hepatitis C virus (HCV), which was not recognized as an infectious agent until the 1980s, is responsible for a worldwide epidemic. The World Health Organization estimates global prevalence at 2.8%, with 185 million persons infected. In contrast to hepatitis B, where successful vaccine campaigns have reduced the disease burden, much less progress has been made toward the control of HCV. Phylogenetic studies suggest that HCV originated in Africa and has been endemic in some regions for at least 500-600 years. However, little is known about the epidemiology, transmission, and clinical course of HCV in Africa. With the advent of highly effective anti-HCV agents, there exists great potential to at least curb the global epidemic. For regions such as sub-Saharan Africa, however, this will require a thorough understanding of the regional population-level epidemiology, risk factors, and transmission mechanisms. Only then can effective treatment and prevention strategies be introduced.

Research paper thumbnail of High Frequency of Active HCV Infection Among Seropositive Cases in West Africa and Evidence for Multiple Transmission Pathways

Clinical Infectious Diseases, 2014

Background. Sub-Saharan Africa (SSA) has one of the highest global hepatitis C virus (HCV) preval... more Background. Sub-Saharan Africa (SSA) has one of the highest global hepatitis C virus (HCV) prevalence estimates. However, reports that suggest high rates of serologic false positives and low levels of viremia have led to uncertainty regarding the burden of active infection in this region. Additionally, little is known about the predominant transmission risk factors in SSA.

Research paper thumbnail of Impact of westernization on fibroblast growth factor 23 levels among individuals of African ancestry

Nephrology Dialysis Transplantation, 2014

The Western diet is associated with high consumption of processed foods preserved with phosphate.... more The Western diet is associated with high consumption of processed foods preserved with phosphate. Higher dietary phosphate consumption stimulates production of fibroblast growth factor 23 (FGF23), which heightens risk for cardiovascular disease and mortality. We hypothesized that adults living in a more westernized society have higher levels of FGF23 due to increased phosphate consumption as measured by urinary phosphate excretion. We measured plasma C-terminal FGF23 levels and urinary phosphate and creatinine levels in timed urine collections among 100 African adults living in the rural area of Igbo-Ora, Nigeria (52 women, 48 men), and 100 African Americans (32 women, 68 men) living in Maywood, IL, an urban suburb of Chicago, IL, USA. Among these 200 participants, urine collections were adequate in 76 and 68 of the Maywood and Igbo-Ora participants, respectively. In the total group, the mean age and body mass index, respectively, were 34.6 ± 8.2 years and 22.1 ± 3.9 kg/m(2) in Igbo-Ora, and 42.8 ± 7.2 years and 25.8 ± 6.5 kg/m(2) in Maywood. Demographic characteristics for each site were very similar after excluding participants without adequate urine collections. Among all 200 participants, the median (interquartile range) FGF23 levels were significantly higher in Maywood versus Igbo-Ora [63.8 (45.0-89.9) versus 12.5 RU/mL (8.5-18.5); P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001] and these differences did not change substantially after excluding nine women from Maywood with FGF23 levels &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;400 RU/mL or after excluding participants with inadequate urine collections. Among participants with adequate urine collections, the mean 24-h urinary phosphate excretion was significantly higher in Maywood versus Igbo-Ora (810.6 ± 309.0 versus 347.5 ± 153.1 mg; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and FGF23 levels correlated significantly with total urinary phosphate excretion (r = 0.62; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and urinary phosphate-to-creatinine ratios (r = 0.50; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Living in a more westernized society may be associated with greater net phosphate absorption, as reflected by higher urinary phosphate excretion, and higher FGF23 levels.

Research paper thumbnail of Elevated hypertension risk for African-origin populations in biracial societies

Journal of Hypertension, 2015

Objectives: Blood pressures in persons of African descent exceed those of other racial/ethnic gro... more Objectives: Blood pressures in persons of African descent exceed those of other racial/ethnic groups in the United States. Whether this trait is attributable to the genetic factors in African-origin populations, or a result of inadequately measured environmental exposures, such as racial discrimination, is not known. To study this question, we conducted a multisite comparative study of communities in the African diaspora, drawn from metropolitan Chicago, Kingston, Jamaica, rural Ghana, Cape Town, South Africa, and the Seychelles.

Research paper thumbnail of Vitamin D levels are low in adult patients with sickle cell disease in Jamaica and West Africa

BMC Hematology, 2014

Background: Patients with sickle cell disease in the USA have been noted to have lower levels of ... more Background: Patients with sickle cell disease in the USA have been noted to have lower levels of vitamin Dmeasured as 25-hydroxyvitamin D (25(OH)D)compared to controls. Average serum 25(OH)D levels are also substantially lower in African Americans than whites, while population distributions of 25(OH)D among Jamaicans of African descent and West Africans are the same as among USA whites. The purpose of this study was to examine whether adult patients with sickle cell disease living in tropical regions had reduced 25(OH)D relative to the general population. Methods: We analyzed serum 25(OH)D in stored samples collected from studies in Jamaica and West Africa of adult patients with sickle cell disease and adult population controls. Results: In samples of 20 Jamaicans and 50 West Africans with sickle cell disease mean values of 25(OH)D were 37% and 39% lower than controls, respectively. Metabolic abnormalities in the absorption and conversion pathways are possible causes for the consistent relative deficiency of 25(OH)D in sickle cell disease. Conclusions: Low 25(OH)D levels in tropical Africa where the burden of sickle cell disease is highest, deserve further investigation, and a randomized trial is warranted to address efficacy of supplementation.

Research paper thumbnail of Multimethod Analyses of Discretionary Time Use and Health Behaviors Among Urban Low-Income African-American Adolescents

Journal of Developmental & Behavioral Pediatrics, 2013

Objective: The objective of this pilot study was to examine the relations between discretionary t... more Objective: The objective of this pilot study was to examine the relations between discretionary time (DT) social context, health behaviors (dietary intake and physical activity), and body mass index (BMI) in a sample of urban low-income African-American early adolescents. Methods: Multiple methods were used, including accelerometers, 24-hour dietary recalls, anthropometric measurements, and Experience Sampling Method (ESM). Participants included 9 boys (mean 5 12.9 years) and 16 girls (mean 5 12.9 years). Sixteen participants were at a healthy weight (10 girls and 6 boys), and 9 were overweight or obese (5 girls and 3 boys). Results: Eighth graders had higher BMI z scores, engaged in less healthful eating during DT, and spent less time in vigorous exercise in DT than sixth graders. Participants spent the majority of DT with siblings, which was associated with increased light physical activity as measured by accelerometers. The ESM data suggested that adolescents engaged in increased physical activity and decreased sedentary activity when with peers but increased sedentary activity when with parents. Increased percentage of DT spent with parents was associated with increased daily fat intake. Data also indicate high consumption of unhealthy foods across all DT social contexts and activities. Conclusions: Peers may provide a protective social context with regard to obesity-related health behaviors. Targeting changes in health behaviors during the middle school years may be an effective means of decreasing obesity risk among urban African-American adolescents. Interventions for urban African-American early adolescents may benefit from facilitating physical activity with peers and targeting change in family health behaviors. (J Dev Behav Pediatr 34:589-598, 2013) Index terms: minority health, health behavior, body mass index, pediatric obesity, physical activity.

Research paper thumbnail of Very low levels of energy expenditure among pre-adolescent Mexican-American girls

International Journal of Pediatric Obesity, 2008

We assessed activity energy expenditure (AEE) in Mexican-American (MA) and European-American (EA)... more We assessed activity energy expenditure (AEE) in Mexican-American (MA) and European-American (EA) children. Total energy expenditure (TEE) and resting energy expenditure (REE) were measured using doubly labeled water (DLW), from which AEE and physical activity level (PAL) were calculated. Groups were comparable for age, sex and body mass index (BMI). REE was not different among groups. The boys did not differ in TEE, AEE, or PAL (MA vs. EA, respectively: TEE, 7.9 ± 1.5 vs. 7.5 ± 0.9 MJ.d −1 , AEE: 64.9 ± 24.7 vs. 65.3 ± 22.3 kJ.kg −1 .d −1 ; PAL: 1.57 ± 0.18 vs. 1.58 ± 0.19 kJ.kg −1 .d −1 ). MA girls had lower TEE, AEE, and PAL than EA girls (total EE: 6.8 ± 0.9 vs. 8.1 ± 0.8 MJ.d −1 ; AEE, 37.3 ± 15.9 vs. 64.9 ± 24.7 kJ.kg −1 .d −1 ; PAL, 1.40 ± 0.12 vs. 1.57 ± 0.18; P<0.005). Results suggest that these MA girls were expending less energy than EA children of comparable body size due to reduced activity energy expenditure.

Research paper thumbnail of Meta-Analysis of Genome-Wide Linkage Studies in Celiac Disease

Research paper thumbnail of Daily activity patterns of 2316 men and women from five countries differing in socioeconomic development

Chronobiology International, 2015

Daily rhythmicity in the locomotor activity of laboratory animals has been studied in great detai... more Daily rhythmicity in the locomotor activity of laboratory animals has been studied in great detail for many decades, but the daily pattern of locomotor activity has not received as much attention in humans. We collected waist-worn accelerometer data from more than 2000 individuals from five countries differing in socioeconomic development and conducted a detailed analysis of human locomotor activity. Body mass index (BMI) was computed from height and weight. Individual activity records lasting 7 days were subjected to cosinor analysis to determine the parameters of the daily activity rhythm: mesor (mean level), amplitude (half the range of excursion), acrophase (time of the peak) and robustness (rhythm strength). The activity records of all individual participants exhibited statistically significant 24-h rhythmicity, with activity increasing noticeably a few hours after sunrise and dropping off around the time of sunset, with a peak at 1:42 pm on average. The acrophase of the daily rhythm was comparable in men and women in each country but varied by as much as 3 h from country to country. Quantification of the socioeconomic stages of the five countries yielded suggestive evidence that more developed countries have more obese residents, who are less active, and who are active later in the day than residents from less developed countries. These results provide a detailed characterization of the daily activity pattern of individual human beings and reveal similarities and differences among people from five countries differing in socioeconomic development. 650 Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only. Chronobiology International Chronobiol Int Downloaded from informahealthcare.com by University of Toronto on 06/17/15 For personal use only.

Research paper thumbnail of 25-hydroxyvitamin D levels in African American and Nigerian women

American Journal of Human Biology, 2013

Americans have substantially lower levels of circulating 25(OH)D than whites. We compared populat... more Americans have substantially lower levels of circulating 25(OH)D than whites. We compared population-based samples of 25(OH)D in women of African descent from Nigeria and metropolitan Chicago.

Research paper thumbnail of The long isoform uncoupling protein-3 (UCP3L) in human energy homeostasis

International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity, 1999

The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon ami... more The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon amino acid sequence homology to UCP1. Spontaneous mutations of UCP3> have been described in humans, but not in rodents. The functional consequences-or lack thereof-of these mutations in humans will be of great importance in elucidating the biology of this protein. The results of two such studies are summarized here.

Research paper thumbnail of A genome-wide linkage analysis investigating the determinants of blood pressure in whites and African Americans

American journal of hypertension, 2003

Evidence for genomic regions influencing systolic and diastolic blood pressure (BP) were assessed... more Evidence for genomic regions influencing systolic and diastolic blood pressure (BP) were assessed in a whole genome linkage analysis in 211 African American and 160 white families as part of the GenNet network of the National Heart, Lung and Blood Institute-sponsored Family Blood Pressure Program. Multipoint regression and variance components linkage methods were used to analyze 372 polymorphic markers. Statistically compelling evidence for linkage (P values .0057 and .00023, respectively) was found on chromosome 1. Our results support the idea that BP regulation is most likely governed by multiple genetic loci, each with a relatively weak effect on BP in the population at large.

Research paper thumbnail of Linkage disequilibrium and haplotype diversity in the genes of the renin-angiotensin system: findings from the family blood pressure program

Genome research, 2003

Association studies of candidate genes with complex traits have generally used one or a few singl... more Association studies of candidate genes with complex traits have generally used one or a few single nucleotide polymorphisms (SNPs), although variation in the extent of linkage disequilibrium (LD) within genes markedly influences the sensitivity and precision of association studies. The extent of LD and the underlying haplotype structure for most candidate genes are still unavailable. We sampled 193 blacks (African-Americans) and 160 whites (European-Americans) and estimated the intragenic LD and the haplotype structure in four genes of the renin-angiotensin system. We genotyped 25 SNPs, with all but one of the pairs spaced between 1 and 20 kb, thus providing resolution at small scale. The pattern of LD within a gene was very heterogeneous. Using a robust method to define haplotype blocks, blocks of limited haplotype diversity were identified at each locus; between these blocks, LD was lost owing to the history of recombination events. As anticipated, there was less LD among blacks, ...

Research paper thumbnail of An international comparative study of blood pressure in populations of European vs. African descent

BMC medicine, 2005

The consistent finding of higher prevalence of hypertension in US blacks compared to whites has l... more The consistent finding of higher prevalence of hypertension in US blacks compared to whites has led to speculation that African-origin populations are particularly susceptible to this condition. Large surveys now provide new information on this issue. Using a standardized analysis strategy we examined prevalence estimates for 8 white and 3 black populations (N = 85,000 participants). The range in hypertension prevalence was from 27 to 55% for whites and 14 to 44% for blacks. These data demonstrate that not only is there a wide variation in hypertension prevalence among both racial groups, the rates among blacks are not unusually high when viewed internationally. These data suggest that the impact of environmental factors among both populations may have been under-appreciated.

Research paper thumbnail of Comparisons of intensity-duration patterns of physical activity in the US, Jamaica and 3 African countries

BMC Public Health, 2014

Background: This difference in how populations living in low-, middle or upper-income countries a... more Background: This difference in how populations living in low-, middle or upper-income countries accumulate daily PA, i.e. patterns and intensity, is an important part in addressing the global PA movement. We sought to characterize objective PA in 2,500 participants spanning the epidemiologic transition. The Modeling the Epidemiologic Transition Study (METS) is a longitudinal study, in 5 countries. METS seeks to define the association between physical activity (PA), obesity and CVD risk in populations of African origin: Ghana (GH), South Africa (SA), Seychelles (SEY), Jamaica (JA) and the US (suburban Chicago). Methods: Baseline measurements of objective PA, SES, anthropometrics and body composition, were completed on 2,500 men and women, aged 25-45 years. Moderate and vigorous PA (MVPA, min/d) on week and weekend days was explored ecologically, by adiposity status and manual labor. Results: Among the men, obesity prevalence reflected the level of economic transition and was lowest in GH (1.7%) and SA (4.8%) and highest in the US (41%). SA (55%) and US (65%) women had the highest levels of obesity, compared to only 16% in GH. More men and women in developing countries engaged in manual labor and this was reflected by an almost doubling of measured MPVA among the men in GH (45 min/d) and SA (47 min/d) compared to only 28 min/d in the US. Women in GH (25 min/d), SA (21 min/d), JA (20 min/d) and SEY (20 min/d) accumulated significantly more MPVA than women in the US (14 min/d), yet this difference was not reflected by differences in BMI between SA, JA, SEY and US. Moderate PA constituted the bulk of the PA, with no study populations except SA men accumulating > 5 min/d of vigorous PA. Among the women, no sites accumulated >2 min/d of vigorous PA. Overweight/obese men were 22% less likely to engage in manual occupations. Conclusion: While there is some association for PA with obesity, this relationship is inconsistent across the epidemiologic transition and suggests that PA policy recommendations should be tailored for each environment.

Research paper thumbnail of Distribution of metals exposure and associations with cardiometabolic risk factors in the “Modeling the Epidemiologic Transition Study”

Environmental Health, 2014

Background: The vitamin D-endocrine system is thought to play a role in physiologic processes tha... more Background: The vitamin D-endocrine system is thought to play a role in physiologic processes that range from mineral metabolism to immune function. Serum 25-hydroxyvitamin D [25(OH)D] is the accepted biomarker for vitamin D status. Skin color is a key determinant of circulating 25(OH)D concentrations, and genes responsible for melanin content have been shown to be under strong evolutionary selection in populations living in temperate zones. Little is known about the effect of latitude on mean concentrations of 25(OH)D in dark-skinned populations. Objective: The objective was to describe the distribution of 25(OH)D and its subcomponents in 5 population samples of African origin from the United States, Jamaica, Ghana, South Africa, and the Seychelles. Design: Participants were drawn from the Modeling of the Epidemiologic Transition Study, a cross-sectional observational study in 2500 adults, ages 25-45 y, enrolled between January 2010 and December 2011. Five hundred participants, w50% of whom were female, were enrolled in each of 5 study sites: Chicago, IL (latitude: 418N); Kingston, Jamaica (178N); Kumasi, Ghana (68N); Victoria, Seychelles (48S); and Cape Town, South Africa (348S). All participants had an ancestry primarily of African origin; participants from the Seychelles trace their history to East Africa. Results: A negative correlation between 25(OH)D and distance from the equator was observed across population samples. The frequency distribution of 25(OH)D in Ghana was almost perfectly normal (Gaussian), with progressively lower means and increasing skewness observed at higher latitudes. Conclusions: It is widely assumed that lighter skin color in populations outside the tropics resulted from positive selection, driven in part by the relation between sun exposure, skin melanin content, and 25(OH)D production. Our findings show that robust compensatory mechanisms exist that create tolerance for wide variation in circulating concentrations of 25(OH)D across populations, suggesting a more complex evolutionary relation between skin color and the vitamin D pathway. This trial was registered at clinicaltrials.gov as NCT02111902.

Research paper thumbnail of 25-Hydroxyvitamin D in African-origin populations at varying latitudes challenges the construct of a physiologic norm

American Journal of Clinical Nutrition, 2014

Background: The vitamin D-endocrine system is thought to play a role in physiologic processes tha... more Background: The vitamin D-endocrine system is thought to play a role in physiologic processes that range from mineral metabolism to immune function. Serum 25-hydroxyvitamin D [25(OH)D] is the accepted biomarker for vitamin D status. Skin color is a key determinant of circulating 25(OH)D concentrations, and genes responsible for melanin content have been shown to be under strong evolutionary selection in populations living in temperate zones. Little is known about the effect of latitude on mean concentrations of 25(OH)D in dark-skinned populations. Objective: The objective was to describe the distribution of 25(OH)D and its subcomponents in 5 population samples of African origin from the United States, Jamaica, Ghana, South Africa, and the Seychelles. Design: Participants were drawn from the Modeling of the Epidemiologic Transition Study, a cross-sectional observational study in 2500 adults, ages 25-45 y, enrolled between January 2010 and December 2011. Five hundred participants, w50% of whom were female, were enrolled in each of 5 study sites: Chicago, IL (latitude: 418N); Kingston, Jamaica (178N); Kumasi, Ghana (68N); Victoria, Seychelles (48S); and Cape Town, South Africa (348S). All participants had an ancestry primarily of African origin; participants from the Seychelles trace their history to East Africa. Results: A negative correlation between 25(OH)D and distance from the equator was observed across population samples. The frequency distribution of 25(OH)D in Ghana was almost perfectly normal (Gaussian), with progressively lower means and increasing skewness observed at higher latitudes. Conclusions: It is widely assumed that lighter skin color in populations outside the tropics resulted from positive selection, driven in part by the relation between sun exposure, skin melanin content, and 25(OH)D production. Our findings show that robust compensatory mechanisms exist that create tolerance for wide variation in circulating concentrations of 25(OH)D across populations, suggesting a more complex evolutionary relation between skin color and the vitamin D pathway. This trial was registered at clinicaltrials.gov as NCT02111902.

Research paper thumbnail of Association between smoking and total energy expenditure in a multi-country study

Nutrition & Metabolism, 2014

Background: The association between smoking and total energy expenditure (TEE) is still controver... more Background: The association between smoking and total energy expenditure (TEE) is still controversial. We examined this association in a multi-country study where TEE was measured in a subset of participants by the doubly labeled water (DLW) method, the gold standard for this measurement. Methods: This study includes 236 participants from five different African origin populations who underwent DLW measurements and had complete data on the main covariates of interest. Self-reported smoking status was categorized as either light (<7 cig/day) or high (≥7 cig/day). Lean body mass was assessed by deuterium dilution and physical activity (PA) by accelerometry.

Research paper thumbnail of Under-reporting of dietary energy intake in five populations of the African diaspora

British Journal of Nutrition, 2015

Studies on the role of diet in the development of chronic diseases often rely on self-report surv... more Studies on the role of diet in the development of chronic diseases often rely on self-report surveys of dietary intake. Unfortunately, many validity studies have demonstrated that self-reported dietary intake is subject to systematic under-reporting, although the vast majority of such studies have been conducted in industrialised countries. The aim of the present study was to investigate whether or not systematic reporting error exists among the individuals of African ancestry (n 324) in five countries distributed across the Human Development Index (HDI) scale, a UN statistic devised to rank countries on non-income factors plus economic indicators. Using two 24 h dietary recalls to assess energy intake and the doubly labelled water method to assess total energy expenditure, we calculated the difference between these two values ((self-report 2 expenditure/expenditure) £ 100) to identify under-reporting of habitual energy intake in selected communities in Ghana, South Africa, Seychelles, Jamaica and the USA. Under-reporting of habitual energy intake was observed in all the five countries. The South African cohort exhibited the highest mean under-reporting (252·1 % of energy) compared with the cohorts of Ghana (222·5 %), Jamaica (2 17·9 %), Seychelles (2 25·0 %) and the USA (2 18·5 %). BMI was the most consistent predictor of underreporting compared with other predictors. In conclusion, there is substantial under-reporting of dietary energy intake in populations across the whole range of the HDI, and this systematic reporting error increases according to the BMI of an individual.

Research paper thumbnail of Physical activity and pre-diabetes—an unacknowledged mid-life crisis: findings from NHANES 2003–2006

PeerJ, 2014

The prevalence of pre-diabetes (PD) among US adults has increased substantially over the past two... more The prevalence of pre-diabetes (PD) among US adults has increased substantially over the past two decades. By current estimates, over 34% of US adults fall in the PD category, 84% of whom meet the American Diabetes Association's criteria for impaired fasting glucose (IFG). Low physical activity (PA) and/or sedentary behavior are key drivers of hyperglycemia. We examined the relationship between PD and objectively measured PA in NHANES 2003-2006 individuals between 20 and 65 yrs.We excluded all participants without IFG measures or adequate accelerometry data (final N = 1,317). Participants were identified as PD if FPG was 100-125 mg/dL (5.6-6.9 mmol/L). Moderate and vigorous PA in minutes/day individuals were summed to create the exposure variable "moderate-vigorous PA" (MVPA). The analysis sample included 884 normoglycemic persons and 433 with PD. There were significantly fewer PD subjects in the middle (30.3%) and highest (24.6%) tertiles of PA compared to the lowest tertile (35.5%). After adjusting for BMI, participants were 0.77 times as likely to be PD if they were in the highest tertile compared to the lowest PA tertile (p < 0.001). However, these results were no longer significant when age and BMI were held constant. Univariate analysis revealed that physical activity was associated with decreased fasting glucose of 0.5 mg/dL per minute of MVPA, but multivariate analysis adjusting for age and BMI was not significant. Overall, our data suggest a negative association between measures of PA and the prevalence of PD in middle-aged US adults independent of adiposity, but with significant confounding influence from measures of BMI and age. Assah FK, Brage S, Ekelund U, Wareham NJ. 2008. The association of intensity and overall level of physical activity energy expenditure with a marker of insulin resistance. Diabetologia 51(8):. Dela F, Mikines KJ, Von Linstow M, Secher NH, Galbo H. 1992. Effect of training on insulin-mediated glucose uptake in human muscle. A, Coen P, Goodpaster BH. 2011. Effects of weight loss and exercise on insulin resistance, and intramyocellular triacylglycerol, diacylglycerol and ceramide. Diabetologia 54(5):Pharmacological and lifestyle interventions to prevent or delay type 2 diabetes in people with impaired glucose tolerance: systematic review and meta-analysis. BMJ 334(7588):299-307 Helmerhorst HJ, Wijndaele K, Brage S, Wareham NJ, Ekelund U. 2009. Objectively measured sedentary time may predict insulin resistance independent of moderate-and vigorous-intensity physical activity. Diabetes 58(8):. 2008. Efficacy of a theory-based behavioural intervention to increase physical activity in an at-risk group in primary care (ProActive UK): a randomised trial. Lancet 371(9606):41-48

Research paper thumbnail of Hepatitis C in sub-saharan Africa: urgent need for attention

Open forum infectious diseases, 2014

The hepatitis C virus (HCV), which was not recognized as an infectious agent until the 1980s, is ... more The hepatitis C virus (HCV), which was not recognized as an infectious agent until the 1980s, is responsible for a worldwide epidemic. The World Health Organization estimates global prevalence at 2.8%, with 185 million persons infected. In contrast to hepatitis B, where successful vaccine campaigns have reduced the disease burden, much less progress has been made toward the control of HCV. Phylogenetic studies suggest that HCV originated in Africa and has been endemic in some regions for at least 500-600 years. However, little is known about the epidemiology, transmission, and clinical course of HCV in Africa. With the advent of highly effective anti-HCV agents, there exists great potential to at least curb the global epidemic. For regions such as sub-Saharan Africa, however, this will require a thorough understanding of the regional population-level epidemiology, risk factors, and transmission mechanisms. Only then can effective treatment and prevention strategies be introduced.

Research paper thumbnail of High Frequency of Active HCV Infection Among Seropositive Cases in West Africa and Evidence for Multiple Transmission Pathways

Clinical Infectious Diseases, 2014

Background. Sub-Saharan Africa (SSA) has one of the highest global hepatitis C virus (HCV) preval... more Background. Sub-Saharan Africa (SSA) has one of the highest global hepatitis C virus (HCV) prevalence estimates. However, reports that suggest high rates of serologic false positives and low levels of viremia have led to uncertainty regarding the burden of active infection in this region. Additionally, little is known about the predominant transmission risk factors in SSA.

Research paper thumbnail of Impact of westernization on fibroblast growth factor 23 levels among individuals of African ancestry

Nephrology Dialysis Transplantation, 2014

The Western diet is associated with high consumption of processed foods preserved with phosphate.... more The Western diet is associated with high consumption of processed foods preserved with phosphate. Higher dietary phosphate consumption stimulates production of fibroblast growth factor 23 (FGF23), which heightens risk for cardiovascular disease and mortality. We hypothesized that adults living in a more westernized society have higher levels of FGF23 due to increased phosphate consumption as measured by urinary phosphate excretion. We measured plasma C-terminal FGF23 levels and urinary phosphate and creatinine levels in timed urine collections among 100 African adults living in the rural area of Igbo-Ora, Nigeria (52 women, 48 men), and 100 African Americans (32 women, 68 men) living in Maywood, IL, an urban suburb of Chicago, IL, USA. Among these 200 participants, urine collections were adequate in 76 and 68 of the Maywood and Igbo-Ora participants, respectively. In the total group, the mean age and body mass index, respectively, were 34.6 ± 8.2 years and 22.1 ± 3.9 kg/m(2) in Igbo-Ora, and 42.8 ± 7.2 years and 25.8 ± 6.5 kg/m(2) in Maywood. Demographic characteristics for each site were very similar after excluding participants without adequate urine collections. Among all 200 participants, the median (interquartile range) FGF23 levels were significantly higher in Maywood versus Igbo-Ora [63.8 (45.0-89.9) versus 12.5 RU/mL (8.5-18.5); P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001] and these differences did not change substantially after excluding nine women from Maywood with FGF23 levels &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;400 RU/mL or after excluding participants with inadequate urine collections. Among participants with adequate urine collections, the mean 24-h urinary phosphate excretion was significantly higher in Maywood versus Igbo-Ora (810.6 ± 309.0 versus 347.5 ± 153.1 mg; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and FGF23 levels correlated significantly with total urinary phosphate excretion (r = 0.62; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and urinary phosphate-to-creatinine ratios (r = 0.50; P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Living in a more westernized society may be associated with greater net phosphate absorption, as reflected by higher urinary phosphate excretion, and higher FGF23 levels.

Research paper thumbnail of Elevated hypertension risk for African-origin populations in biracial societies

Journal of Hypertension, 2015

Objectives: Blood pressures in persons of African descent exceed those of other racial/ethnic gro... more Objectives: Blood pressures in persons of African descent exceed those of other racial/ethnic groups in the United States. Whether this trait is attributable to the genetic factors in African-origin populations, or a result of inadequately measured environmental exposures, such as racial discrimination, is not known. To study this question, we conducted a multisite comparative study of communities in the African diaspora, drawn from metropolitan Chicago, Kingston, Jamaica, rural Ghana, Cape Town, South Africa, and the Seychelles.

Research paper thumbnail of Vitamin D levels are low in adult patients with sickle cell disease in Jamaica and West Africa

BMC Hematology, 2014

Background: Patients with sickle cell disease in the USA have been noted to have lower levels of ... more Background: Patients with sickle cell disease in the USA have been noted to have lower levels of vitamin Dmeasured as 25-hydroxyvitamin D (25(OH)D)compared to controls. Average serum 25(OH)D levels are also substantially lower in African Americans than whites, while population distributions of 25(OH)D among Jamaicans of African descent and West Africans are the same as among USA whites. The purpose of this study was to examine whether adult patients with sickle cell disease living in tropical regions had reduced 25(OH)D relative to the general population. Methods: We analyzed serum 25(OH)D in stored samples collected from studies in Jamaica and West Africa of adult patients with sickle cell disease and adult population controls. Results: In samples of 20 Jamaicans and 50 West Africans with sickle cell disease mean values of 25(OH)D were 37% and 39% lower than controls, respectively. Metabolic abnormalities in the absorption and conversion pathways are possible causes for the consistent relative deficiency of 25(OH)D in sickle cell disease. Conclusions: Low 25(OH)D levels in tropical Africa where the burden of sickle cell disease is highest, deserve further investigation, and a randomized trial is warranted to address efficacy of supplementation.

Research paper thumbnail of Multimethod Analyses of Discretionary Time Use and Health Behaviors Among Urban Low-Income African-American Adolescents

Journal of Developmental & Behavioral Pediatrics, 2013

Objective: The objective of this pilot study was to examine the relations between discretionary t... more Objective: The objective of this pilot study was to examine the relations between discretionary time (DT) social context, health behaviors (dietary intake and physical activity), and body mass index (BMI) in a sample of urban low-income African-American early adolescents. Methods: Multiple methods were used, including accelerometers, 24-hour dietary recalls, anthropometric measurements, and Experience Sampling Method (ESM). Participants included 9 boys (mean 5 12.9 years) and 16 girls (mean 5 12.9 years). Sixteen participants were at a healthy weight (10 girls and 6 boys), and 9 were overweight or obese (5 girls and 3 boys). Results: Eighth graders had higher BMI z scores, engaged in less healthful eating during DT, and spent less time in vigorous exercise in DT than sixth graders. Participants spent the majority of DT with siblings, which was associated with increased light physical activity as measured by accelerometers. The ESM data suggested that adolescents engaged in increased physical activity and decreased sedentary activity when with peers but increased sedentary activity when with parents. Increased percentage of DT spent with parents was associated with increased daily fat intake. Data also indicate high consumption of unhealthy foods across all DT social contexts and activities. Conclusions: Peers may provide a protective social context with regard to obesity-related health behaviors. Targeting changes in health behaviors during the middle school years may be an effective means of decreasing obesity risk among urban African-American adolescents. Interventions for urban African-American early adolescents may benefit from facilitating physical activity with peers and targeting change in family health behaviors. (J Dev Behav Pediatr 34:589-598, 2013) Index terms: minority health, health behavior, body mass index, pediatric obesity, physical activity.

Research paper thumbnail of Very low levels of energy expenditure among pre-adolescent Mexican-American girls

International Journal of Pediatric Obesity, 2008

We assessed activity energy expenditure (AEE) in Mexican-American (MA) and European-American (EA)... more We assessed activity energy expenditure (AEE) in Mexican-American (MA) and European-American (EA) children. Total energy expenditure (TEE) and resting energy expenditure (REE) were measured using doubly labeled water (DLW), from which AEE and physical activity level (PAL) were calculated. Groups were comparable for age, sex and body mass index (BMI). REE was not different among groups. The boys did not differ in TEE, AEE, or PAL (MA vs. EA, respectively: TEE, 7.9 ± 1.5 vs. 7.5 ± 0.9 MJ.d −1 , AEE: 64.9 ± 24.7 vs. 65.3 ± 22.3 kJ.kg −1 .d −1 ; PAL: 1.57 ± 0.18 vs. 1.58 ± 0.19 kJ.kg −1 .d −1 ). MA girls had lower TEE, AEE, and PAL than EA girls (total EE: 6.8 ± 0.9 vs. 8.1 ± 0.8 MJ.d −1 ; AEE, 37.3 ± 15.9 vs. 64.9 ± 24.7 kJ.kg −1 .d −1 ; PAL, 1.40 ± 0.12 vs. 1.57 ± 0.18; P<0.005). Results suggest that these MA girls were expending less energy than EA children of comparable body size due to reduced activity energy expenditure.