Body mass index is a strong predictor of overall mortality

Body mass index (BMI) is a strong predictor of overall mortality above and below the apparent optimum of about 22.5 to 25 kg/m². By avoiding a further increase from 28 kg/m² to 32 kg/m², for example, a person in middle age typically would gain about 2 years of life expectancy.

Whitlock and coworkers analyzed BMI and mortality data from 894,576 adults in 57 studies. BMI was greatest for men and women aged 50 to 69 years.

For both sexes, mortality was lowest for persons with a BMI in the normal range of 22.5 to 25 kg/m². Each 5 kg/m² above this minimum was associated with a 30% jump in mortality. The increase was 40% in vascular conditions (ischemic heart disease, heart failure, hypertension, and stroke); 60% to 120% in diabetic, renal, or hepatic disorders; 10% for cancer; and 20% for respiratory disease. Life expectancy declined by 2 to 4 years at a BMI of 30 to 35 kg/m² and by 8 to 10 years at a BMI of 40 to 45 kg/m².

The authors noted that below 22.5 to 25 kg/m², an overall inverse association with BMI mainly is the result of strong inverse associations for smoking-related respiratory disease.