Those who are extremely obese may live 10 years shorter than they should have lived, according to researchers in UK as quoted by media reports Wednesday.

The researchers examined the findings of 57 studies involving about 900,000 adults from the United States and Europe and followed them for 10 to 15 years. About 70,000 of the participants died in the course of the study.

An overweight pedestrian sits on a wall outside the Houses of Parliament in London in this file photo. [Xinhua/Reuters]

 They used the BMI (body mass index) measures and found that those who are about 40 or more pounds (some 18 kg) over a healthy weight may cut about three years off their lives, mostly from heart disease and stroke. Those who are extremely obese, about 100 or more pounds over a healthy weight, could be shortening their lives by as many as 10 years.

Being extremely obese is similar to the effect of lifelong smoking, said Richard Peto, one of the lead researchers and a professor of medical statistics at Oxford University in England.

Above a healthy weight, every 5-point increase in BMI increases the risk of early death by about 30 percent. People with a BMI between 25 and 29.9, which means they are overweight but not obese, could be shortening their life span by a year.

It "provides a much clearer picture of the risk associated with various levels of being overweight or obese," said Michael Thun, emeritus vice president of epidemiological research at the American Cancer Society.

"Once you gain weight, it's hard to lose it and easy to gain more," said Thun, therefore, to stop weight gain became much more important.

(Agencies via Xinhua March 18, 2009)