Body mass index and mortality – the risks of being obese

A new study was published in The Lancet this month, which looked at body mass index (BMI) and cause-specific mortality in almost 900,000 adults.

BMI is a reasonably good measure of how overweight or obese a person is, and is calculated by dividing the weight in kilograms by height in metres squared. A value of over 25 is classified as overweight, and over 30 is obese.

In this latest study, the Prospective Studies Collaboration undertook analyses of baseline BMI versus mortality in 57 prospective studies with 894,576 participants, mostly from western Europe and North America.

Results showed that in both sexes, mortality was lowest at a BMI of about 22.5-25. For each increase of 5 in BMI there was, on average, about a 30% higher all-cause mortality (40% for vascular; 60-120% for diabetic, renal and hepatic; 10% for neoplastic; and 20% for respiratory and all other mortality).

The authors conclude that in adult life, it is easier to avoid substantial weight gain than to lose weight once it has been gained. By avoiding an increase from a BMI of 28 to a BMI of 32, a typical person in early middle age would gain about 2 years of life expectancy.

For more details about this study, a copy of this paper is available by loging in to the resource library of this website