Excess Deaths Associated With Underweight, Overweight, and Obesity

This study was an attempt to estimate deaths associated with being underweight (body mass index BMI less than 18.5 kg/m2), overweight (BMI 25–29 kg/m2), and obese (BMI 30 or higher kg/m2). Relative mortality risks associated with different BMI levels were estimated from 3 National Health and Nutrition Examination Survey (NHANES) trials covering the years 1971–1975 (NHANES I), 1976–1980 with follow up through 1992 (NHANES II), and 1988–1994 with follow up through 2000 (NHANES III), respectively. Relative risk estimates were applied to the distribution of BMI and other covariates from NHANES 1999–2002 to estimate mortality risk while adjusting for possible confounding factors, including age. Deaths in the NHANES I, II, and III trials totalled 3923, 2133, and 2793, respectively. Obesity was associated with an increased mortality risk, especially for younger subjects. Relative risk was low in overweight individuals. Relative risk figures for underweight persons generally exceeded unity. A similar pattern was evident for each of the 3 surveys. Although a BMI of 35 kg/m2 or above was relatively infrequent, these individuals accounted for a majority of obesity-related excess deaths in the year 2000. The relative mortality risk associated with obesity was higher in NHANES I than in the other 2 trials. Compared with normal-weight subjects, those who were overweight had a slight reduction in mortality. Of the 111,909 excess deaths associated with obesity, a majority occurred in persons less than 70 years of age. The opposite was the case for underweight persons. In NHANES surveys dating back to 1971, both underweight and obesity—especially a high degree of obesity—are associated with increased mortality compared with normal-weight persons. Possibly better medical care and improved public health measures have lessened the effect of obesity on mortality. The findings are in accord with increased life expectancy in the United States and with decreasing mortality from ischemic heart disease.