Lancet Editors' note: Around the world, increasing body-mass index (BMI) is a major public concern. Rightly so, according to this international collaborative analysis of almost 1 million people, followed from middle age in 57 prospective studies. A J-shaped mortality curve is observed, with optimal survival at a BMI of 22•5–25 kg/m2. Above this range, mortality from several causes—especially vascular diseases—was increased. Moderate obesity (BMI 30–35) was associated with 3 years’ loss of life. People with extreme obesity (BMI 40–50) lost 10 years of life, equivalent to the years lost by lifetime smoking.
Findings
In both sexes, mortality was lowest at about 22·5—25 kg/m2. Above this range, positive associations were recorded for several specific causes and inverse associations for none, the absolute excess risks for higher BMI and smoking were roughly additive, and each 5 kg/m2 higher BMI was on average associated with about 30% higher overall mortality.
Below the range 22·5—25 kg/m2, BMI was associated inversely with overall mortality, mainly because of strong inverse associations with respiratory disease and lung cancer. These inverse associations were much stronger for smokers than for non-smokers, despite cigarette consumption per smoker varying little with BMI.
Interpretation
Although other anthropometric measures (eg, waist circumference, waist-to-hip ratio) could well add extra information to BMI, and BMI to them, BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22·5—25 kg/m2. The progressive excess mortality above this range is due mainly to vascular disease and is probably largely causal. At 30—35 kg/m2, median survival is reduced by 2—4 years; at 40—45 kg/m2, it is reduced by 8—10 years (which is comparable with the effects of smoking). The definite excess mortality below 22·5 kg/m2 is due mainly to smoking-related diseases, and is not fully explained.
Diagrams, list of studies & causes of death
Optimum BMI for men: 23.5
BMI Optimum: 22.5
BMI Optimum: 22.5
BMI Optimum 27.5
BMI Optimum 23
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