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Body Mass Index Above Ideal Range Linked to Large Increase in Mortality Rate

March 17, 2009 - Body-mass index (BMI) above the ideal range may cause a large increase in mortality rates, according to the results of a collaborative analysis of 57 prospective studies reported in the March 18 issue of Lancet.

"The main associations of…BMI with overall and cause-specific mortality can best be assessed by long-term prospective follow-up of large numbers of people," write Gary Whitlock, and colleagues from The Prospective Studies Collaboration at the University of Oxford, Oxford, United Kingdom. "The Prospective Studies Collaboration aimed to investigate these associations by sharing data from many studies."

The investigators analyzed the association of baseline BMI with mortality (death) in 57 prospective studies enrolling a total of 894,576 participants, mostly in western Europe and North America, with median recruitment year 1979. Mean age at recruitment was 46 ± 11 years, 61% were men, and mean BMI was 25 ± 4.

Mortality rate was lowest with BMI at approximately 22.5 to 25 for both men and women. At higher baseline BMI, there were positive associations for several specific causes. Absolute risks for higher BMI and smoking were approximately additive.

On average, each 5 point higher BMI was associated with approximately 30% higher overall mortality rate.

"...BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22.5–25," the study authors write. "At 30–35 BMI, median survival is reduced by 2–4 years; at 40–45 BMI, it is reduced by 8–10 years (which is comparable with the effects of smoking)."

"In adult life, it may be easier to avoid substantial weight gain than to lose that weight once it has been gained," the study authors conclude. "By avoiding a further increase from 28 to 32, a typical person in early middle age would gain about 2 years of life expectancy. Alternatively, by avoiding an increase from 24 to 32 (ie, to a third above the apparent optimum), a young adult would on average gain about 3 extra years of life."

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