The Gangwon Obesity and Metabolic Syndrome Study: Methods and Initial Baseline Data (original) (raw)

Enrollment of the study population

The first baseline cohort survey of the GOMS study was designed to recruit 300 Korean adults aged 40−69 years living in the western inland region of Gangwon province (Yeongseo). This region is marked by high mountains and plateaus with deep valleys, and the obesity prevalence of the region is higher than that in other regions. The rationales for the inclusion criteria of age were as follows: (1) the incidences of chronic diseases increase significantly after the age of 40 years and (2) there are different characteristics of obesity in people aged ≥70 years compared to obesity in the general population. The first survey was conducted in the period of June 18 to July 3, 2022, in Hongcheon district and between July 9 to 24, 2022, in Inje district of Gangwon province (Fig. 1). We excluded (1) subjects who were Korean-illiterate and (2) subjects with moderate or severe cognitive dysfunction.

The recruitment was publicized through diverse tools. The recruitment notice was published both online and offline. It contained study information with inclusion criteria, contact phone numbers, and a QR code by which residents of that area could show their interest in participation. It was issued in local life information magazines and at community facilities, local hospitals, and local public health agencies. Onsite registration was also available. Finally, 153 participants from Hongcheon and 164 participants from Inje district (totaling 317 residents) participated in the cohort baseline survey.

Sample size calculations

We obtained a statistical power of 88% for detecting differences between the two study groups (36% of participants had BMI ≥23 kg/m2 vs. 64% of participants had BMI <23 kg/m2) in the two-sample t-test using the sample size of 300, assuming that the mean triglyceride levels were 127 mg/dL and 176 mg/dL, respectively, with a 130 mg/dL standard deviation.12 For logistic regression, if the probabilities of elevated triglyceride levels were 15% for participants with mean BMI values and 28% for those with mean plus standard deviation BMI values, the inclusion of 119 participants would result in a statistical power of >85%. Therefore, a sample size of 300 would be expected to have a statistical power of >85%.

Assessment of lifestyle factors, socioeconomic status, and comorbidities

Demographic data, lifestyle information, body weight changes, medical history, psychological status, and dietary data were assessed using a self-administered questionnaire (Table 1).13-31 The survey questionnaires were delivered to the participants in advance or given onsite, who filled them out by themselves. Considering the filled-in questionnaire, trained researchers interviewed participants to complete missing questions or rectify the wrong answers. Each participant’s interview took about 0.5–1 hour.

The questionnaire included sociodemographic variables related to obesity (marital status, education level, house income, occupation, etc.) and behavioral factors (smoking, alcohol drinking, physical activity, etc.). Types of marital status included single, married, separated, widowed, divorced, and other. Education was divided into the following seven levels: no education, elementary, middle school, high school, college, university, and graduate school. Monthly household income was divided into the following five levels: <2.0, 2.0–4.0, 4.0–6.0, 6.0–8.0, and ≥8.0 million Korean won. Occupation types included manager, professional, office worker, service worker, sales worker, agricultural/forestry/fishery worker, simple labor, military, housewife, unemployed, and other.

Regarding behavioral factors, smoking, the usage of electronic cigarettes, alcohol drinking, exercise, physical activity, sleep pattern, and chronotype14-16 were investigated. A questionnaire for smoking investigated the usage of general cigarettes, “heat-not-burn” cigarettes, and electronic cigarettes. For alcohol drinking, the type of alcohol, the frequency of drinking, the typical amount of alcohol consumed, and the maximum amount of alcohol consumed in a day were explored. Types, frequency, intensity, and duration of exercise and physical activity were evaluated. In order to assess detailed lifestyle and social environment factors in the rural community, we assessed the seasonal variation of physical activities, food addiction,17,18 the status of food security,19 the community environment of food and walking,20-22 the social network,23 and farming activities.

Dietary data were obtained by a validated food frequency questionnaire that has been previously used in the Korea National Health and Nutrition Examination Survey.31 Past medical history records were assessed for hypertension, dyslipidemia, ischemic heart disease, stroke, diabetes, thyroid disease, and cancer. For women, menstrual and reproductive history, breastfeeding, and usage of artificial estrogen hormone were assessed based on the self-reported answer to the relevant question. The survey questionnaire also covered depression,24,25 anxiety,26,27 and quality of life28-30 to determine their psychological status.

The selection of questionnaires was performed by experts of relevant fields, who referred to previous surveys such as the Korea National Health and Nutrition Examination Survey and the Korean Genome and Epidemiology Study (KoGES). The Korean versions of questionnaires on depression,24,25 anxiety,26,27 morningness–eveningness,13-16 food addiction,17 quality of life,28-30 and the food frequency questionnaire31 adopted in this study have been validated in previous studies. The composition of the whole survey questionnaire, specific questionnaires used in the survey, and their validity studies in the Korean language are shown in Table 1.

Anthropometric measurements

Height, weight, waist circumference (WC), and hip circumference were measured by well-trained investigators. Height was measured in the erect position with a tape measure to the nearest 0.1 cm. Body weight was measured while wearing light clothes with bare feet using a bioelectrical impedance analysis device (ACCUNIQ BC720; SELVAS Healthcare, Daejeon, Korea) to the nearest 0.1 kg, and waist and hip circumferences were measured with a tape measure to the nearest 0.1 cm. WC was measured at the midpoint between the lower margin of the rib cage and the upper margin of the iliac creast, and hip circumference was measured with the most protruding part of the hip horizontally. Body composition, including body fat mass (kg), lean body mass (kg), and body fat percentage (%), was assessed by bioelectrical impedance analysis (ACCUNIQ BC720; SELVAS Healthcare). After taking enough rest, the blood pressure (BP) and pulse rate were measured twice in a sitting position using an automatic sphygmomanometer (BP500; SELVAS Healthcare), and the average value was used.

Hand grip strength test

Hand grip strength was evaluated using a digital hand dynamometer (TKK-5401; TAKEI, Tokyo, Japan) in both hands in a standing position with neutral positioning of the wrist and forearm and an extended elbow.

Blood tests

Blood collection was performed under fasting and smoking cessation for ≥2 hours and abstinence from alcohol for ≥2 days by trained health professional personnel. The complete blood cell count and serum levels of glucose, insulin, glycosylated hemoglobin (HbA1c), total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, aspartate aminotransferase, alanine transaminase, high-sensitivity C-reactive protein, thyroid-stimulating hormone, gamma-glutamyl transferase, albumin, total protein, creatinine, carotenoids (carotene, cryptoxanthin, lutein, zeaxanthin, and lycopene), retinoids, and tocopherol were assessed. Participants’ extra blood samples were stored at −75°C in deep freezers of the Korean Society for the Study of Obesity and the Korean Institute of Nutrition at Hallym University for future research. The storage process was carried out according to the general introduction of storage presented by the International Society for Biological and Environmental Repositories.

Skin keratin examination

Adhesive tape (D-squame tape; CuDerm Corp., Dallas, TX, USA) was placed on the upper anterior forearms, subjected to a constant pressure, and peeled off twice on the same spot. This method was used to collect lipids and probiotics in the keratin of the skin. This is a non-invasive inspection method that is performed by attaching the tape and then peeling it off immediately. Through this, skin lipid metabolites and skin lactic acid probiotics bacteria can be analyzed.

Stool test and gut microbiome analysis

Participants were provided a fecal kit in advance to collect feces on the morning of the survey date or the previous day. Participants were instructed to collect a sample at least the size of their thumbnail. Comprehensive analysis of gut microbiota was planned to be conducted with the collected fecal samples.

Definitions

For this study, a current smoker referred to someone who has smoked >5 packs (100 cigarettes) in their lifetime and has smoked in the last month, and a current drinker was defined as someone who drank alcohol more than once a month.

BMI was classified into six categories, as follows: <18.5 (underweight), 18.5–22.9 (normal), 23.0–24.9 (pre-obesity), 25.0–29.9 (class I obesity), 30.0–34.9 (class II obesity), and ≥35.0 kg/m2 (class III obesity). Additionally, central obesity was defined as WC ≥90 cm for men and ≥85 cm for women according to the Korean Society for the Study of Obesity.32

Metabolic syndrome (MS) was defined according to a joint interim statement of the International Diabetes Federation Task Force on Epidemiology and Prevention; the National Heart, Lung, and Blood Institute; the American Heart Association; the World Heart Federation; the International Atherosclerosis Society; and the International Association for the Study of Obesity,33 with Korean-specific cutoff values of WC set according to the Korean Society for the Study of Obesity.32 Broadly, an individual should have ≥3 of the following criteria to be diagnosed with MS: (1) WC ≥90 cm for men or ≥85 cm for women; (2) triglycerides ≥150 mg/dL or taking dyslipidemia drugs; (3) HDL cholesterol <40 mg/dL for men or <50 mg/dL for women; (4) systolic BP ≥130 mmHg, diastolic BP ≥85 mmHg, or treatment of previously diagnosed hypertension; and (5) fasting plasma glucose ≥100 mg/dL or treatment of previously diagnosed type 2 DM.

Hypertension was defined by systolic BP ≥140 mmHg, diastolic BP ≥90 mmHg, or taking hypertension drugs.34 DM was defined by fasting glucose ≥126 mg/dL, HbA1c ≥6.5%, or taking diabetes drugs.35 Dyslipidemia was defined by a serum level of (1) total cholesterol ≥240 mg/dL, (2) triglycerides ≥200 mg/dL, (3) serum HDL cholesterol <40 mg/dL in men or <50 mg/dL in women, (4) serum LDL cholesterol ≥160 mg/dL, or (5) taking dyslipidemia drugs.36

Statistical analyses

Data are presented as mean±standard deviation values or as a number (percentage), unless indicated otherwise. To compare the baseline characteristics between men and women, the chi-squared test and independent-samples t-test were used. All statistical analyses were performed using Stata 17.0 (StataCorp., College Station, TX, USA). A two-tailed P-value of <0.05 was considered statistically significant.

Ethics statement

The protocol for this study was reviewed and approved by the Institutional Review Board of Hallym University (No. HIRB-2021-077-2-RR). The study objectives were explained to the participants and written informed consent was obtained.