I wrote back in January about the large numbers of studies that are publicized in the media that doctors and patients are better off ignoring. I usually try not to give these studies any attention, but this week a study got so much media coverage that I felt I had to tell you all to ignore it.
This study in the journal Circulation looked at participants in the Framingham Heart Study (a large study of heart disease risk factors that started in the 1940s) and looked to see if a link existed between soft drink consumption and the metabolic syndrome. The metabolic syndrome is a collection of factors (abdominal obesity, elevated blood glucose, elevated blood pressure, elevated triglycerides, and low HDL) that increase the risk of developing diabetes and heart disease. The study found that those who drank soft drinks were at higher risk of developing the metabolic syndrome than those who didn’t, even if those drinks were diet (non-caloric artificially sweetened) drinks. This apparently surprising finding generated much media coverage including this article in the Washington Post.
The problem with this study is the same as the problem with all the studies we should ignore. It was an observational study, not an experiment. (Check out my January 5 post if you need a refresher on the difference between observational studies and experiments.) The study didn’t tell some people to drink soft drinks and some people to drink tap water. It simply observed what they were already doing. So the study can’t suggest that soda drinking causes the metabolic syndrome, just that the two things tend to happen in the same people.
There is no likely mechanism through which diet sodas can cause the metabolic syndrome. What is much more likely is that people who tend to be heavier tend to like drinking sweet drinks, so they drink more soft drinks (both diet and regular) than skinny people. So soda drinking almost certainly doesn’t cause metabolic syndrome. A drive to consume sweets is likely behind both soda drinking and the metabolic syndrome. So please, ignore this study.
I’m grateful to my patients Luetrell T. and David D. for sending me links to articles about this study.