Body-mass index and mortality risk in U.S. blacks compared to whites

Abstract

Objective: To compare body-mass index (BMI)-related mortality risk in U.S. Blacks vs. Whites as the relationship appears to differ across race/ethnicity groups.

Methods: Cross-sectional surveys of nationally representative samples of 11,934 Blacks and 59,741 Whites aged 35-75 in the National Health Interview Survey from 1997 to 2002 with no history of cardiovascular disease (CVD) or cancer were pooled. Mortality follow-up was available through 2006. BMI was calculated from self-reported height and weight. We used adjusted Cox regression analysis to adjust for potential confounders.

Results: Over 9 years of follow-up, there were 4303 deaths (1205 among never smokers). Age-adjusted mortality rates were higher in Blacks compared to Whites at BMI < 25 kg/m2 and showed no increase at higher levels of BMI. In men, adjusted hazard ratios for all-cause death rose in a similar fashion across upper BMI quintiles in Blacks and Whites; in women, however, BMI was positively associated with mortality risk in Whites, but inversely associated in Blacks (P interaction = 0.01). Racial disparities were amplified in subsidiary analyses that introduced a 12-month lag for mortality or focused on CVD mortality.

Conclusions: The relationship of elevated BMI to mortality appeared weaker in US Blacks than in Whites, especially among women.

Figure 1. Composition of the Analytic Sample

NHIS=National Health Interview Survey from 1997 to 2002 with mortality follow-up until 2006; NH=Non-Hispanic; *Missing data on smoking, cancer, heart disease, or mortality status; All participant characteristics have less than 10% missing values. Not sampled=not randomly selected to participate in sample adult file that has more extensive health data than family file

Figure 2. Age-standardized All-Cause Mortality Rates (per 1000 person-years) through 2006 for (1) 32,975 Never Smokers and (2) 38,700 Ever Smokers Aged 35 to 75 Years without a History of Heart Disease or Cancer at Baseline, by Race, Sex, and Body-Mass Index Quintile

Bars indicate upper or lower 95% confidence intervals.

Figure 3. Adjusted Hazard Ratios for Death from Any Cause among 1) 32,975 Never Smokers and 2) 38,700 Ever Smokers Aged 35 to 75 without Heart Disease or Cancer at Baseline by Race, Sex, and Body-Mass Index Quintile

Error bars indicate upper or lower 95% confidence intervals Hazard ratios were obtained using Cox proportional hazards models adjusted for age (as the timescale), alcohol consumption, leisure-time physical activity, educational attainment (less than high school, high school, some college, college or more), and marital status. Each race-sex specific group uses its respective quintile 2 as the reference *Indicates p<0.05 for comparison to quintile 2 for each separate race-sex group p for linear trend for quintile 2 through quintile 5: 0.09 (White men) and 0.25 (White women) p for Race-BMI

Figure 4. Adjusted Hazard Ratios for All-Cause Mortality (Censoring Deaths in the First 12 Months of Follow-Up) in 32,975 Never Smokers Aged 35 to 75 without Heart Disease or Cancer by Race, Sex, and Body-Mass Index Quintile

Hazard ratios were obtained using Cox proportional hazards models adjusted for age (as the timescale), alcohol consumption, leisure-time physical activity, educational attainment (less than high school, high school, some college, college or more), and marital status. Each race-sex specific group uses its respective quintile 2 as the reference *indicates p<0.05 for comparison to quintile 2; p for linear trend above quintile 2 is p=0.08 (White men); 0.95 (Black men); 0.20 (White women); 0.30 (Black women); p for Race-BMI interaction: 0.12 (men) and 0.03 (women)