Carrying around even a few extra kilos may shorten your life, according to a study that advises people to avoid weight gain.

It is known that middle-aged people who are obese face an increased risk of death. However, it has been less clear if that risk extended to people with just a few extra kilos.

A new study by the US National Cancer Institute says if you are in your fifties and are slightly overweight, your chances of dying during the next 10 years are 20 percent to 40 percent higher, reported online edition of health magazine WebMD.

Michael F. Leitzmann and other researchers who studied half a million Americans also found that the risk of death is applicable to healthy people with no history of smoking, even if they were only overweight at age 50, it said.

Participants were between the ages of 50 and 71 at enrolment, and were studied for 10 years.

The researchers relied on self-reported estimates of current weight, and weight at age 50, taken from a questionnaire filled by participants.

There were 61,317 deaths during the 10-year follow-up, with the overall risk of death highest among subjects who had the highest and lowest body weights as determined by body mass index (BMI), a ratio based on height and weight.

Someone with a BMI of less than 18.5 is considered to be underweight. A BMI of 18.5 to 24.9 is considered normal; 25 to 29.9 considered overweight; and 30 or greater is considered obese.

For example, a 5.7-foot person would be considered overweight, but not obese, at a weight between 160 pounds (72.73 kg) and 190 pounds (86.36 kg). Someone six feet tall who weighs between 185 (84.09 kg) and 220 pounds (100 kg) would also meet the BMI classification for overweight but not obese.

The issue is of critical importance to the aging population of the US, where one in three adults are obese and another third are considered overweight.

"This study contributes in an important way to understanding the risks of being overweight from the standpoint of early mortality," Leitzmann was quoted as saying.