Women who drink more than one sweetened soft drink a day are slightly more likely to develop diabetes than women who drink less than one a month, according to a new study.

But critics of the study noted the same conclusion might be drawn from examining eating habits involving other forms of junk food, too.

Obesity is strongly linked to type 2 diabetes (search) — the most common form of diabetes — so the extra calories from soda account for at least some of the increased risk, said the Harvard University (search) researchers who did the study. But the scientists said there also appears to be a link to the way the body handles the sugars in soft drinks — a claim two outside experts said needs more research.

A soft drink trade group said the study's conclusions were not scientifically sound and that the focus should be on the unhealthy lifestyles and weight gain that can lead to diabetes — not soft drinks.

Globally, type 2 diabetes, a condition that often leads to heart disease and kidney failure, afflicts 154 million people and is blamed for about 3 millions deaths a year.

The soft drink study, which appears in Tuesday's Journal of the American Medical Association, involved an analysis of data from a continuing health study of 51,603 female nurses.

Researchers analyzed surveys filled out by the nurses in 1991, 1995 and 1999 detailing their eating habits, weight, physical activity and other health issues. There were 741 new cases of type 2 diabetes during the span.

Researchers found that women drinking one or more sugar-sweetened soft drinks a day were twice as likely to develop diabetes as women who drank fewer than one a month. Even when they considered such factors as weight, diet and lifestyle differences, the researchers still found that women drinking sugary sodas were 1.3 times as likely to develop diabetes.

That led the scientiests to suggest that in addition to extra calories, the beverages might also increase diabetes risk because their high amount of rapidly absorbed sugars causes a dramatic rise in glucose and insulin concentrations in the body, said Dr. Walter Willett, one of the study's co-authors.

"I think there is a very practical implication of this study, both for weight control and for type 2 diabetes — keep soda consumption low," said Willett, chairman of the Department of Nutrition at the Harvard School of Public Health (search).

Fruit juice consumption was not associated with diabetes risk, and diet soft drinks were not statistically significant, but sugared fruit punch showed similar results to sugared soda.

Two diabetes experts not associated with the study said it was well conducted, but they cautioned against making a direct connection between the sugars found in soda and diabetes risk without more research.

Still, Dr. Caroline M. Apovian said the study should encourage doctors to ask patients about their soda consumption as a way to gauge potential weight gain and a diet heavy on empty calories. Apovian, associate professor of medicine at Boston University School of Medicine (search), wrote an accompanying JAMA editorial.

Karmeen Kulkarni of the American Diabetes Association (search) said similar results might be found if researchers studied another food with little nutritional value, such as chips, cakes or cookies.

She said women in the study who drink more sugary beverages tended to live a less healthy lifestyle — smoking more, working out less, eating more calories and less fiber and protein. The research also relied on the women to write down what they ate, making it less reliable.

Those same drawbacks were cited by the American Beverage Association's (search) Richard Adamson, who called the study's conclusions "not scientifically based."

"I think a careful reading leads to a conclusion that it's really an unhealthy lifestyle, not sweetened beverages, that increases the risk of type 2 diabetes," said Adamson, the association's vice president of scientific and technical affairs.