This study examined the association of body mass index (BMI) with cause-specific mortality. Data were taken from the National Health and Nutrition Examination Survey (NHANES) for the years 1971–1980 and 1988–1994, with mortality follow-up through 2000. Person-years of follow-up totalling 571,042 were combined with data from NHANES 1999–2002. Cause of death information was available for 2.3 million adults aged 25 and older. BMI categories included underweight (BMI less than 18.5), overweight (BMI of 25–29), and obese (BMI of 30 and above).
Obesity but not overweight was significantly and positively associated with excess mortality from cardiovascular disease (CVD). The association held for coronary heart disease and other cardiovascular causes such as stroke. No significant association was found between excess mortality and BMI categories. Analysis of non-CVD, noncancer mortality disclosed an association with being underweight. Overweight was associated with significantly decreased mortality from causes other than CVD and cancer. Obesity was associated with significantly increased mortality from CVD but not with cancer nor noncancer, non-CVD mortality. Overweight and obesity combined were associated with increased mortality from diabetes and kidney disease and with decreased mortality from other noncancer, non-CVD mortality. Obesity was associated with increased mortality from cancers considered to be obesity-related. The association of obesity with CVD mortality appeared to decrease over time.
In this large-scale survey, being overweight was associated with significantly decreased all-cause mortality overall. The findings affirm that relationships between BMI and mortality vary considerably with the cause of death.