Body mass index (BMI) is a measure of someone’s weight in relation to height; to calculate one’s BMI, multiply one’s weight in pounds and divide that by the square of one’s height in inches; overweight is a BMI greater than 25; obese is a BMI greater than 30. A collaborative analysis of 57 prospective studies reported in the March 18 Online First issue of Lancet. 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.On average, each 5-kg/m² higher BMI was associated with approximately 30% higher overall mortality rate. 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.”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.”

Comments: This is an easy index to use. There are several web pages that will calculate BMI. Try this one http://www.nhlbisupport.com/bmi/. Although this index has a lot of shortcomings, it is easy to monitor. Please note that the study measured weight in kilograms and height in meters. BA