SCIENTISTS like to remind us not to confuse cause and effect. But they’re not immune from making that mistake themselves. Last week, for example, the mass media reported a Harvard University study that has exonerated diet sodas and other artificially-sweetened beverages from previous studies linking their consumption to diabetes.
“This is such a great example of confusing cause and effect. It’s akin to saying ‘playing basketball makes you tall’ because height and basketball are correlated. Of course, the real answer is that taller people play basketball,” says Dr. Josh Bloom of the American Council on Science and Health.
The new study ‒ published in The American Journal of Clinical Nutrition ‒ indicates that the link is a result of other factors common to both diet soda drinkers and people with diabetes, including that they are more likely to be overweight. In other words, people who are already diabetic or overweight are drinking more diet soda for those very reasons.
The Harvard University researchers, who followed a large group of men for 20 years, found that drinking regular soda and other sugary drinks often meant a person was more likely to get diabetes, but that was not true of artificially-sweetened soft drinks, or coffee or tea.
They found that men who drank the most sugar-sweetened beverages ‒ about one serving a day on average ‒ were 16 percent more likely to be diagnosed with diabetes than men who never drank those beverages. The link was mostly due to soda and other carbonated beverages, and drinking non-carbonated sugar-sweetened fruit drinks such as lemonade was not linked with a higher risk of diabetes.
When nothing else was accounted for, men who drank a lot of diet soda and other diet drinks were also more likely to get diabetes. But once researchers took into account men’s weight, blood pressure, and cholesterol, those drinks were not related to diabetes risk.
Replacing sugary drinks with diet versions seems to be a safe and healthy alternative, the authors say. “There are multiple alternatives to regular soda,” says Dr. Frank Hu, one of the study’s authors, adding, “Diet soda is perhaps not the best alternative, but moderate consumption is not going to have appreciable harmful effects.”
When asked to comment on the study, Dr. Rebecca Brown, an endocrinologist at the National Institutes of Health, who has studied artificial sweeteners but was not involved in the Harvard research, told Reuters Health: “People who are at risk for diabetes or obesity…those may be the people who are more likely to choose artificial sweeteners because they may be more likely to be dieting.”
Hu and his colleagues analyzed data from more than 40,000 men who were followed between 1986 and 2006. During that time, participants regularly filled out questionnaires on their medical status and dietary habits, including how many servings of regular and diet sodas and other drinks they consumed every week. About 7 percent of men reported that they were diagnosed with diabetes at some point during the study.
The study also found that drinking coffee on a daily basis ‒ both regular and decaffeinated ‒ was linked to a lower risk of diabetes. Researchers aren’t sure why that is, but it could be due to antioxidants or vitamins and minerals in coffee, Hu said.
Brown said that while there are still some health concerns about artificial sweeteners, none have been proven. “I certainly think that we have better evidence that drinking sugar-sweetened beverages increases health risks,” Brown said, adding, “Certainly, reducing sugar-sweetened beverage consumption by any means (including substitution with diet drinks) is probably a good thing.”