Settling the Diet Soda and Dementia Debate — For Now

Does diet soda have a dementia link? Despite the occasional media frenzy over whether Diet Coke causes Alzheimer’s, here’s what the existing, credible, published research actually says.

Diet soda: By ditching the high sugar content and replacing it with artificial sweeteners, it’s supposed to be a healthier alternative to classic pop. Yet it always seems to get a bad wrap. Browsing the Internet, diet sodas appear to be linked to every disease under the sun, from cancer to diabetes. Despite these allegations, artificial sweeteners have been studied for decades, with dozens of studies supporting their overall safety as food additives. This didn’t stop the development of a new myth surrounding diet soda and dementia from going viral: In 2017, a study published in Stroke led dozens of news outlets to claim that diet sodas tripled the risk of developing stroke or Alzheimer’s. 

Just look at some of these alarming headlines: Why Is Diet Soda So Bad for Your Brain?, Trump’s 12 Diet Cokes a Day Could Be Really Bad For You, and Drink a Diet Coke, Get a STROKE Claims Surprising Research. Suffice it to say, these headlines are much more confident about the conclusions than the study’s authors. No, this one isolated piece of research did not prove that diet soda caused or increased risk of developing Alzheimer’s. Let’s take a closer look at what it actually did find.

So, is diet soda actually bad for the brain?

The 2017 study on the artificial sweeteners used in soda drinks like Diet Coke looked at 2,888 people over the age of 45 to assess whether drinking regular and diet soda puts people at higher risk of having a stroke. They also looked at 1,484 people over the age of 60 to see whether soda affects the risk of developing dementia. The study used self-reporting through a survey called a food frequency questionnaire to estimate how often people drank diet or regular soda.

While they found that people who drank diet sodas had triple the risk of developing stroke or Alzheimer’s, the authors of the study weren’t certain about the direction of cause and effect. 

People who drank more diet soda had a higher prevalence of hypertension, diabetes and cardiovascular disease. Does that mean diet soda is the root cause of these diseases? There is no way, from this research, to tell. But there is certainly the possibility that someone who drinks a lot of diet soda might be trying to cut back on sugars because they are already aware of certain health issues — or myriad other variables. 

Several researchers published criticisms in response to the study, pointing out problems in the statistical analysis and self-reported food questionnaire, and casting doubt on the validity of the findings. (For the uninitiated, this is as close as scientists get to a rap battle — using references to scientific studies instead of rhymes.) 

Without getting into the nuts and bolts of the statistical methods, it is safe to say that the study does not convincingly establish any link between diet soda and dementia. 

It is also important to note that only one other study on diet soda and cognition has been conducted since then, coming to the opposite conclusion: Rather, people drinking regular soda — not diet soda — were the group that was more likely to develop cognitive decline over the course of six years. These findings, however, did not receive nearly as much media attention.

A couple observational studies on something as notoriously difficult to measure as the health risk of a single element in a much broader diet don’t make a strong case for switching from one soda to the other. But if you’re tempted to give up soda altogether for a healthier option, unsweetened tea, or black coffee may be better bets. There’s no solid evidence that tea or coffee are good for your brain health, but humans have been enjoying them for centuries. Everything in moderation.