MIAMI, United States (AFP) — Most adults gain weight as they age, but adding as little as 11 pounds (five kilograms) by middle age may substantially raise the risk of major illnesses, US researchers said Tuesday.

Harvard University scientists found that even modest weight gain in adulthood “was associated with a significantly elevated incidence of a composite measure of major chronic diseases, consisting of type 2 diabetes, cardiovascular disease, cancer, and nontraumatic death,” said the report in the Journal of the American Medical Association.

“Our study is the first of its kind to systematically examine the association of weight gain from early to middle adulthood with major health risks later in life,” said senior author Frank Hu, professor of nutrition and epidemiology at Harvard University.

“The findings indicate that even a modest amount of weight gain may have important health consequences.”

The study was based on survey data from more than 92,000 people, tracked from 1976 until 2012.

Participants self-reported their estimated weight gains, beginning from age 18 in women and age 21 in men, through 55, an age researchers described as “middle adulthood.”

Most people gained weight over that span. Women added an average of 22 pounds (10 kilos) and men about 19 pounds (8.6 kilos).

But compared to people who maintained their weight within five pounds of their young adult selves, those who bulked up faced significant increases in health problems, from heart disease to unhealthy aging, said the report.

“Each five-kilogram (11-pound) weight gain was associated with a 30 percent increased risk of type 2 diabetes,” it said.

Other risks included a 14 per cent increased risk of high blood pressure and eight percent increased risk of cardiovascular disease.

Weight-gainers also saw a six per cent increased risk of obesity-related cancer.

Those who had never smoked saw a five percent increased risk of dying prematurely.

Overall, each 11 pound weight gain was linked to a 17 per cent lower chance of achieving healthy aging.

“Higher amounts of weight gain were associated with greater risk of chronic diseases,” added the report.

Researchers said they hope their findings help doctors and patients better understand the health consequences of gaining weight over time.