Report finds soft drinks increase risk of diabetes

Women who drank at least one sugar-laden soda every day were substantially more likely to develop diabetes and gained significantly more weight than women who avoided the beverages, Harvard researchers report today in a study published amid urgent campaigns to shrink the ballooning American waistline.

Scientists from the Harvard School of Public Health and Brigham and Women's Hospital tracked the health of thousands of female nurses during the 1990s through a detailed questionnaire and discovered that women who regularly consumed soft drinks were 83 percent more likely to develop type 2 diabetes than women who did not. Sugary fruit-flavored drinks were even worse, doubling the risk of the disease.

The study, published in today's Journal of the American Medical Association, concluded that the soda drinkers gained an average of 17 pounds over eight years, compared with an increase of just six pounds by the nurses who avoided soft drinks.

But it's not just the calories that matter in soft drinks and fruit juices: Researchers said that the beverages send a rush of unhealthy sugar directly into the blood, which can disrupt the body's ability to normally process sugar.

Nutrition specialists said the findings could yield important clues to understanding why type 2 diabetes is increasing in both adults and adolescents, who once were rarely diagnosed with a disease that more commonly is seen in middle-aged adults. Soft drink consumption among youths more than doubled from the 1970s to the 1990s.

Already, schools across the nation, including Boston's system, have pulled the plug on vending machines that dispense soft drinks and fruit-flavored beverages, substituting healthier alternatives, including juices, which do not appear to increase the prospects of developing diabetes.

''I was very surprised at how much drinking these sugar-sweetened beverages increases the risk of diabetes," said Karen Chalmers, director of nutrition at Joslin Diabetes Center. ''The public health message here is that it's a waste of calories to drink any of these beverages."

The findings on the link between soft drinks and diabetes were based on surveys completed by more than 91,000 nurses, and researchers took into account other lifestyle factors -- including alcohol consumption, cigarette use, and exercise -- before concluding that soda consumption increased the likelihood of developing type 2 diabetes.

Diet drinks, the researchers report, do not appear to elevate the risk of diabetes.

There are two main types of diabetes. Type 1, also known as juvenile-onset, typically first becomes evident in childhood and requires daily doses of insulin for survival. Type 2, which used to be called adult-onset, is more often linked with health behaviors such as eating too much and, depending on severity, may not require insulin injections.

The US Centers for Disease Control and Prevention reports that from 1980 to 2002 the number of diabetics in the United States more than doubled, to 18 million.

Specialists say that the epidemics of obesity and diabetes are inextricably bound. The vast majority of diabetics suffer from type 2, with about 17 million cases in the United States.

The Harvard scientists said they believe that their study is the first large-scale report to establish a firm association between soft drink consumption and diabetes.

''These sugar-sweetened soft drinks are important contributors to obesity and type 2 diabetes in the United States, and limiting consumption of these beverages could help curb these epidemics," said Dr. JoAnn E. Manson, chief of preventive medicine at Brigham and Women's and an author of the study. ''If people really enjoy these drinks, they may be able to switch to a diet soda, which may not cause the weight gain or the increased risk of type 2 diabetes."

Soft drinks, the Harvard researchers said, are loaded with calories. A 12-ounce can, for example, contains 150 calories. But in the era of super-sizing, the neighborhood convenience store offers 64-ounce cups swimming in 800 calories, fully half of the recommended daily intake of a sedentary woman.

But it's not just the calories that are implicated, scientists said.

''With sugared beverages, it's so easy to take in a big sugar load rapidly, and that's what singles them out as a culprit," said Dr. Meir J. Stampfer, professor of epidemiology and nutrition at Harvard School of Public Health and another author of the study.

While the study did not examine the cellular-level effects of soft-drink consumption, researchers speculated that the infusion of sugar initiates a biochemical cascade that results in a yo-yoing of sugar and insulin in the bloodstream.

That can set the stage for development of diabetes. In type 2 diabetes, the body either stops producing enough insulin or starts ignoring insulin, a hormone that transports sugar needed to fuel the body from the blood into cells.

There may be yet another consequence to consuming so many calories from soft drinks. Liquids, unlike solid food, do not satisfy hunger. The result: While soda drinkers derive a bounty of calories from the drinks, they are not sating their appetite and may not cut down their consumption of calories from food.

A representative of the beverage industry questioned the conclusions the Harvard researchers drew from their data. Richard H. Adamson, vice president for scientific and technical affairs at the American Beverage Association, said that an alternative reading of the data shows that obesity alone could explain most of the increased diabetes risk.

The Harvard researchers responded that the 83 percent increased risk represented the net effect of soft drinks, combining weight gain attributed to the drinks and the consequences of introducing so much sugar so rapidly.

But Adamson said that the causes of obesity are far more complex than how many sodas a person consumes. ''If you eat a lot, you don't exercise, you sit on your butt all day, you're going to gain weight," said Adamson, a toxicologist and former official of the National Institutes of Health. ''There's nothing magical about a soft drink. A piece of white bread could contribute to the calories."

Lawmakers and school boards in Massachusetts have moved aggressively in recent months to ban soft drinks from school campuses. On Beacon Hill, the Joint Committee on Health Care voted unanimously to banish junk food from schools, and Representative Peter J. Koutoujian, chairman of the committee, said he is optimistic the full Legislature will adopt the proposal during the next session.

In June, the Boston School Committee endorsed a measure supporting the elimination of unhealthy offerings from vending machines.

Stephen Smith can be reached at stsmith@globe.com.