You can’t ask people to drink sugar-sweetened beverages and see who develops type 2 diabetes, researcher Vasanti Malik explains. That would be like asking people to smoke when you have good reason to know it might harm them, she said.
So Malik and her colleagues at the Harvard School of Public Health used an alternative to the gold-standard randomized clinical trial for their study appearing online today in the journal Diabetes Care. They pooled the results of 11 studies -- eight on the risk of diabetes and three on the risk of metabolic syndrome among more than 300,000 participants altogether -- to reach conclusions about consuming these beverages and later health problems.
The researchers compared people who drank one to two sweetened soft drinks, fruit drinks, iced tea, energy drinks, or vitamin water every day with people who had one or no sweetened beverage over the course of a month to see which group was more likely to develop type 2 diabetes or metabolic syndrome, a precursor to diabetes that includes high blood sugar, high blood pressure, high abdominal body fat, and high levels of “bad” cholesterol.
After followup ranging from four to 20 years, about 15,000 people were diagnosed with type 2 diabetes and about 5,800 had metabolic syndrome. People who drank the most sugar-sweetened beverages had a 26 percent higher risk of developing type 2 diabetes and a 20 percent higher risk of developing metabolic syndrome compared with people who drank the least. Increasing intake by one 12-ounce soda a day boosted the risk of type 2 diabetes by 15 percent.
“What’s really important is a very clear, significant positive association with the risk of type 2 diabetes,” Malik said in an interview. “There are a lot of factors that contribute to type 2 diabetes, but this is one modifiable factor that would be very easy for people to change.”
The kinds of drinks or the kinds of sugar -- sucrose, high-fructose corn syrup, or fruit juice concentrates -- were not studied separately, but the authors say their metabolic effects are essentially the same. A 100 percent juice drink is not considered sugar-sweetened.
The American Beverage Association disputed the study’s results.
“It is overly simplistic, and simply misleading, to suggest that reducing or eliminating sugar-sweetened beverages from the diet will uniquely lower incidence of serious health conditions such as diabetes or metabolic syndrome,” Dr. Maureen Storey, senior
vice president for science policy for the American Beverage Association, said in an e-mailed statement. “After all, correlations found in epidemiological studies are not indicators of causality. In fact, there is a critical flaw in the design of the studies used in this meta-analysis in that the authors focus solely on the impact of one calorie source – sugar-sweetened beverages – on weight, rather than looking at all sources of calories.”
Malik said the individual studies accounted for known differences between the two groups of people that might explain the different rates of type 2 diabetes and metabolic syndrome.
“Sure, people who drink soda tend to be less physically active, they might eat more saturated fat,” she said. But even after the researchers accounted for weight differences, the association between sweetened drinks and diabetes persisted, she said.
Being overweight puts people at increased risk for type 2 diabetes, and consuming calories in liquid form makes it easier to put on weight, the authors say. They cite a study that compared people who drank sweetened beverages before a meal with people who consumed the same amount of calories from jelly beans. At their next meal, the people who drank their calories ate significantly more than people who ate jelly beans.
Malik said she and her colleagues hope their work will provide stronger evidence for public health policy as schools and communities consider limiting sugar-sweetened beverages, through taxes or bans.
“We’re not saying this is the only factor associated with diabetes, but it’s one [that] can really make an impact if it’s reduced,” she said.
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