Causes of Excess Mortality Associated with Low and High BMIs

Both low and high body-mass indexes are associated with excess risk for short- and long-term death. To further explore the relation between BMI and mortality, Oxford investigators pooled individual data on baseline BMI and subsequent mortality from 57 prospective cohort studies (900,000 participants; 61% male; mean baseline age, 46). Mean follow-up was 8 years following a 5-year blackout period to minimize the effect of reverse causality.

For both sexes and all ages, overall mortality was lowest in people with baseline BMIs between 22.5 kg/m² and 25 kg/m²; it rose by about 30% for each 5-unit rise in BMI above this level and by about 25% for each 5-unit drop in BMI below this level. Mortality from ischemic heart disease rose by about 40% for…