Among black women, the risk of death from any cause is increased for all categories of overweight and obesity, as it is in whites, according to a report in the Sept. 8 issue of the New England Journal of Medicine.
The hazard ratios also are similar in magnitude for black women as for white women and men, said Deborah A. Boggs, Sc.D., of the Slone Epidemiology Center at Boston University, and her associates (N. Engl. J. Med. 2011;365:901-8).
Previous studies of the link between overweight and mortality have included only a limited number of black subjects or have failed to report results on black subjects separately from those on whites, so it was uncertain whether the association was present in black women. Yet the prevalence of obesity and abdominal obesity both have risen fastest in black women, with projections that by 2020, 70% of black women will be obese and 90% will have abdominal obesity, the investigators noted.
Dr. Boggs and her colleagues used data on a subgroup of 51,695 subjects enrolled in the Black Women’s Health Study (BWHS) to examine the relationship between risk of death and both overall and abdominal obesity. They focused their analysis on the 33,916 subjects who had never smoked because this association can be confounded by the effects of smoking.
The BWHS is an ongoing prospective follow-up study of black women across the United States who were aged 21-69 years at enrollment in 1995 and who have been followed every 2 years since then.
The researchers found that the association between body mass index (BMI) and risk of death from any cause was curvilinear: lowest among women with a BMI of 20-25 kg/m2 and rising as BMI approached both the lower and the higher extremes. Mortality risk was increased for every category of BMI in the overweight and obesity range.
Among women with a BMI of 20 or higher, every 5-unit increase in BMI correlated with an 18% rise in the risk of death. "Previous studies involving black women have shown weaker associations of BMI with risk of death," but those studies were small or otherwise flawed, the investigators said.
The higher mortality seen among women with the lowest BMI may have been associated with illness-related weight loss, they added.
Larger waist circumference was not significantly associated with increased risk of death except among nonobese black women. In contrast, previous studies in white women and men found larger waist circumference to predict higher mortality risk, independently of BMI.
The positive association between BMI and risk of death was particularly strong for cardiovascular causes of death. For other causes of death, only a very high BMI was associated with increased risk. And there were no associations between BMI and risk of death from cancer in this study.
The link between BMI and risk of death from all causes was stronger among women with higher levels of education, but not significantly so. Such an association may be more evident among less-educated persons because they have higher absolute risks of death and because of other factors related to low socioeconomic status, such as psychosocial stress and limited access to care, Dr. Boggs and her associates said.
"Previous studies of BMI and risk of death involving blacks have included a greater proportion of less-educated participants. This difference may account in part for the stronger relationship in the present study than that previously reported among blacks," they added.
It is unknown whether the study results can be generalized to black men, the investigators said.
This study was supported by the National Cancer Institute. Dr. Boggs and her associates reported no relevant financial disclosures.