Switching out sugary soda for a sugar-free alternative sounds like an easy way to cut calories, but if you saw a study published in Stroke [1] last week, you may be wondering if you made a mistake. Researchers found that older adults who regularly drank artificially sweetened beverages, such as diet soda, were about three times more likely to have a stroke or develop Alzheimer's disease over 10 years, painting a worrying picture for anyone who regularly enjoys diet soda.
The findings may sound alarming, but the research paints a more nuanced picture. The results come from the Framingham Heart Study, a long-term observational study of people living in Framingham, Massachusetts. From 1991-2001, participants were asked questions about their health and diet. Then, over the following 10 years, the researchers tracked the patients' health, allowing them to cross-reference data and identify associations—including how many people who regularly consumed diet soda developed Alzheimer's disease.
Here's the problem: association doesn't equal causation, and while respected, observational studies cannot determine causation. We can't tell from these results whether drinking diet soda caused Alzheimer's disease. In this population, it's possible that people who chose diet sodas were already at greater risk for the disease. For example, type 2 diabetes is a risk factor for Alzheimer's disease, and people with type 2 diabetes may drink diet soda to limit their sugar intake. In this study, 26% of the diet soda drinkers had diabetes compared to only 9% of non-drinkers. If you adjust for the prevalence of diabetes, the diet soda drinkers had no significant increased risk of Alzheimer's.
It's also important to note that participants were asked about the quality of their diets and lifestyle before the study began, but not in the follow up. And researchers didn't ask about other factors known to influence health, such as socioeconomic status.
While this study does not conclusively show that drinking diet soda directly increases your risk of Alzheimer's disease, it does point to the importance of controlling other risk factors, particularly type 2 diabetes and mid-life obesity [2]. Other observational studies have found that diet soda is associated with higher odds of developing both of these conditions [3][4]. In fact, some preliminary data suggests that consumption of diet soda may impair your body's ability to manage blood glucose levels or even promote overeating, which may lead to type 2 diabetes or obesity [3][5].
So, should you cut out artificial sugars? Though the data is preliminary, it's a good idea to limit these drinks, as long as you don’t replace them with something worse, like sugary sodas. Instead, choose water when you can, as well as drinks that can benefit your brain health and reduce Alzheimer's risk, such as coffee or green tea.
Nick McKeehan is a member of the ADDF's Aging and Alzheimer's Prevention program. He evaluates the scientific evidence for and against therapies to promote brain health and/or prevent Alzheimer's disease at our website CognitiveVitality.org and contributes regularly to the site's blog. Mr. McKeehan previously served as Chief Intern at Mid Atlantic Bio Angels (MABA) and was a research technician at Albert Einstein College of Medicine investigating repair capabilities of the brain. Mr. McKeehan received a bachelor of science degree in biology from Purdue University, where he was awarded a Howard Hughes Scholarship. He also writes about the biotechnology industry for 1st Pitch Life Science.
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