Adiposity as Compared With Physical Activity in Predicting Mortality Among Women

Some believe that improved physical fitness can counter the effects of overweight and obesity on illness and death. If so, the implication is that obesity may be a less important factor in mortality than fitness. The investigators reviewed data on body mass index (BMI) and mortality for 116,564 women participating in the Nurses’ Health Study. In 1976, the women were 30 to 55 years of age and had no known cardiovascular disease or cancer. The 10,282 deaths occurring during 24 years of follow-up included 5223 from cancer and 2370 from cardiovascular disease. A direct relationship between BMI and mortality was evident when only women who had never smoked were analyzed. On multivariate analysis, the relationship held for deaths from cancer and, more strongly, for deaths from cardiovascular causes. Increased mortality correlated significantly with both excess weight/obesity and physical inactivity. Overall mortality for obese women, whose BMI was 30 kg/m2 or higher, was double that for lean women having a BMI less than 25 kg/m2. Deaths from cardiovascular disease were 3 times as high, and cancer mortality was increased 65%. Physical inactivity, defined as less than 1 hour of exercise per week, was associated with a 52% increase in overall mortality and with a doubling of cardiovascular mortality. Overweight and obesity predicted increased mortality independently of the level of physical activity, and higher activity levels did not weaken the association between obesity and mortality. Compared with lean, active women, the relative risk of death was 1.55 for lean, inactive women, 1.91 for obese women who were active, and 2.42 for obese women who were inactive. In the entire cohort, excess weight and physical inactivity together accounted for an estimated 26% of all premature deaths, 47% of deaths from cardiovascular causes, and 16% of deaths from cancer. When analysis was limited to women who had never smoked, the respective figures were 31%, 59%, and 21%. The BMI and the level of physical activity significantly and independently predicted mortality in these middle-aged women, but a high activity level did not eliminate the excess of deaths associated with obesity. In addition, being lean did not counteract the increased mortality associated with inactivity. Public health efforts should emphasize the importance of maintaining healthy body weight and also the need to engage regularly in physical activity.