Overweight and Obesity in Women: Health Risks and Consequences

Frank B. Hu, M.D., Ph.D.

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In This Article

Obesity and Mortality

The relationship between BMI and total mortality typically has been used as the most important criterion for weight guidelines. However, epidemiologic studies on this topic have been fraught with methodologic problems, including failure to control for cigarette smoking; inappropriate control of biologic effects of obesity, such as hypertension and hyperglycemia; and failure to consider weight loss caused by subclinical diseases.[61] These biases have led to the typical J-shaped or U-shaped relationship between BMI and mortality observed in many epidemiologic studies and to a systematic underestimate of the impact of obesity on premature mortality. In the Nurses' Health Study,[62] age-adjusted analyses suggested a J-shaped relation between BMI and overall mortality. When women who had never smoked were examined separately, no increase in risk was observed among the leaner women, and a more direct relation between weight and mortality was observed (p for trend < 0.001) (Fig. 4). In multivariate analyses of women who had never smoked and had recently had stable weight, when the first 4 years of follow-up were excluded, the RRs of death from all causes for increasing categories of BMI (<19.0, 19.0-21.9, 22.0-24.9, 25.0-26.9, 27.0-28.9, 29-31.9, _32) were 1.0, 1.2, 1.2, 1.3, 1.6, 2.1, and 2.2 (p for trend < 0.001). Among women with a BMI of _32.0 who had never smoked, the RR of death from CVD was 4.1 (95% CI, 2.1-7.7), and that of death from cancer was 2.1 (95% CI, 1.4-3.2), compared with the risk among women with a BMI <19.0. A weight gain of _10 kg since the age of 18 was associated with a significantly increased mortality in middle adulthood. These results suggest that body weight was directly related to overall mortality among these middle-aged women, and lean women did not have excess mortality. In a recent analysis of the American Cancer Society cohort who had never smoked,[63] after early deaths were eliminated, mortality increased linearly with increasing BMI ranging from <19.0 to 32 at all ages up to 75 years in both men and women.

Influence of increasing control for methodologic bias on the shape of the curve describing the relation between BMI and RR of death from all causes. The curve progressed from a J shape in age-adjusted analyses of the entire cohort (A) to an increasingly direct association when the analysis was restricted to women who never smoked (B), when early deaths were excluded (C), and when only women with stable weight in the previous 4 years were included (D). (From Manson et al. N Engl J Med 1995;333:677.62)

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