Past body mass index and risk of mortality among women - PubMed (original) (raw)

Past body mass index and risk of mortality among women

S C Moore et al. Int J Obes (Lond). 2008 May.

Abstract

Background: Epidemiologic studies of body mass index (BMI) in relation to mortality commonly exclude persons with health conditions and/or a history of smoking to prevent bias resulting from illness-related weight loss ('reverse causation'). Analysis of BMI from an earlier time period may minimize reverse causation without requiring exclusion of participants based on disease or smoking history.

Methods: We prospectively examined BMI based on technician measurements of weight and height from 10 years prior to start of follow-up in relation to subsequent mortality in a cohort of 50 186 women who were 40-93 years old at baseline in 1987-1989. Deaths were ascertained through the US National Death Index. Proportional hazards regression was used to estimate hazard ratios (HRs) of mortality, adjusted for age, education, race/ethnicity, income, menopausal hormone use, smoking and physical activity.

Results: During 10 years of follow-up through 1997, 5201 women died. Overall, we observed a J-shaped association between BMI and mortality, with increased risk for women who were underweight, overweight or obese. The HRs and 95% confidence intervals of mortality for BMI categories of <18.5, 18.5-20.9, 21.0-23.4 (reference), 23.5-24.9, 25.0-27.4, 27.5-29.9, 30.0-34.9 and 35.0+ kg m(-2) were 1.43 (1.19, 1.72), 1.07 (0.98, 1.17), 1.00 (reference), 1.10 (1.00, 1.20), 1.20 (1.11, 1.31), 1.23 (1.11, 1.37), 1.60 (1.44, 1.77) and 1.92 (1.64, 2.24). There was little evidence that pre-existing conditions (heart disease, diabetes and/or cancer) or smoking history modified the past BMI and mortality relation (P=0.54 and 0.76).

Conclusions: In this large cohort of women, BMI based on technician measurements of weight and height from 10 years prior to baseline showed increased risk for mortality across the range of overweight and obesity, regardless of disease and smoking history. Observed associations between overweight, obesity and mortality in healthy individuals may also apply to persons with a history of disease or smoking.

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Figures

Figure 1

Figure 1. Multivariate relative risks of mortality as related to BMI

In each panel, the lines are cubic restricted spline models depicting the dose-response relationship of BMI to mortality on a continuous basis. Relative risks are indicated by the solid lines, and 95 percent confidence intervals by the gray band. The reference BMI is set at 20.2, which is the BMI at the 12.5th percentile of the cohort. The spline modeling was restricted to BMI values between 16 and 40. Panel A depicts the BMI and mortality relation among 43,649 women with no history of chronic disease at the time of weight assessment, including 3,856 deaths. Chronic disease was defined as any prior diagnosis by a physician of heart-disease, diabetes, or cancer. Panel B shows the BMI and mortality relation among 6,506 women with a history of chronic disease at the time of weight assessment, including 1,342 deaths. Panel C demonstrates the BMI and mortality relation among 2,693 women diagnosed with breast cancer during screening, including 587 deaths.

Figure 2

Figure 2. Life expectancy and years of life lost according to BMI category for women 40 years of age

For each BMI category, the line above shows the estimated life expectancy. We estimated life expectancy from direct adjusted survival curves using proportional hazards models with age as the underlying time metric. The 95% confidence intervals for each BMI category were derived using a bootstrap estimator.

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