Atenção gordos e modelos magrinhas!

5 Abril 2009

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"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 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 kg/m². The analyses were adjusted for age, sex, smoking status, and study, and the first 5 years of follow-up were excluded.

Mortality rate was lowest with BMI at approximately 22.5 to 25 kg/m² for both men and women. At higher baseline BMI, there were positive associations for several specific causes and inverse associations for none. Absolute excess risks for higher BMI and smoking were approximately additive.

On average, each 5-kg/m² higher BMI was associated with approximately 30% higher overall mortality rate (hazard ratio per 5 kg/m² [HR], 1.29; 95% confidence interval [CI], 1.27 -1.32): 40% for vascular mortality (HR, 1.41; 95% CI, 1.37 - 1.45); 60% to 120% for diabetic (HR, 2.16; 95% CI, 1.89 - 2.46), renal (HR, 1.59; 95% CI, 1·27 - 1·99), and hepatic (HR, 1.82; 95% CI, 1·59 - 2·09) mortality; 10% for neoplastic mortality (HR, 1.10; 95% CI, 1.06 - 1.15); and 20% for respiratory (HR, 1.20; 95% CI, 1.07 - 1.34) and all other mortality (HR, 1.20; 95% CI, 1.16 - 1.25).

BMI less than 22·5 to 25 kg/m² was inversely associated with overall mortality rate, primarily because of strong inverse associations with respiratory disease and lung cancer. Although cigarette consumption per smoker varied little with BMI, these inverse associations were much
stronger for smokers vs nonsmokers.

"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 study authors write. "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."

"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 kg/m² to 32 kg/m², a typical person in early middle age would gain about 2 years of life expectancy. Alternatively, by avoiding an increase from 24 kg/m² to 32 kg/m² (ie, to a third above the apparent optimum), a young adult would on average gain about 3 extra years of life."