People who consumed the most artificial sweeteners saw their memory and thinking skills decline 62% faster than people who consumed the least, according to a new study of nearly 13,000 adults. That works out to about 1.6 extra years of brain aging. And the amount that put people in the high group is roughly one can of diet soda a day.
Nearly 13,000 Adults, Eight Years, One Uncomfortable Result
The study, published in Neurology and reported by ScienceDaily, followed 12,772 adults across Brazil. They averaged 52 years old when it began and were tracked for roughly eight years. Researchers at the University of São Paulo, led by Claudia Kimie Suemoto, MD, PhD, had everyone fill out detailed questionnaires about what they ate and drank over the previous year, then used those answers to estimate daily intake of seven sweeteners.
Participants were sorted into three groups. The lowest group averaged 20 milligrams a day. The highest averaged 191 milligrams a day, which, for scale, is about the aspartame in one can of diet soda. One can. Not a pallet of Diet Coke and a lifetime of poor decisions.
Three rounds of cognitive testing followed, at the start, the middle, and the end. The tests covered memory, verbal fluency, working memory, word recall, and processing speed. The kind of stuff you use to remember where you parked, or why you walked into the kitchen.
The Numbers Nobody at the Soda Aisle Wants to Hear
After adjusting for age, sex, high blood pressure, and cardiovascular disease, the heaviest consumers showed a 62% faster decline in overall cognitive performance compared with the lightest. That gap equals about 1.6 additional years of cognitive aging over the study period.
It wasn't only the heavy users. The middle group declined 35% faster than the lowest group, equal to roughly 1.3 extra years. So there's no cozy threshold where you can wave your Zero Sugar can around and feel smug. The effect showed up at moderate levels too.
The researchers are careful about what this means, and so are we. These are changes in test scores, not a direct measurement of biological brain aging. And not everyone who drinks diet soda is headed for a fog of forgotten names.
Six Sweeteners Made the List, One Got a Pass
Of the seven sweeteners examined, six were tied to faster cognitive decline, particularly in memory: aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol. These show up everywhere. Diet sodas, flavored waters, energy drinks, yogurt, low-calorie desserts, and a long list of ultra-processed foods that market themselves as the sensible choice.
Sorbitol had the highest average intake at 64 milligrams a day. It's a sugar alcohol, the kind of ingredient you probably never read on a label because the front of the package was too busy saying "guilt-free."
Tagatose was the exception. No link to cognitive decline showed up. The researchers are clear that this doesn't prove tagatose is safe, only that this study didn't find a connection. One sweetener getting a shrug is not a clean bill of health.
People With Diabetes Took the Hardest Hit
The association was stronger in people with diabetes than in those without it. Read that twice. The population most likely to be steered toward sugar substitutes, by doctors, by dietitians, by the entire marketing apparatus of the low-calorie food industry, showed the strongest signal.
The pattern also split by age. Among adults younger than 60, higher sweetener intake was linked to faster declines in verbal fluency and overall cognitive performance. Researchers found no similar association among people over 60.
That should land hard for the middle-aged crowd who switched to diet everything a decade ago because someone told them it was the responsible move. You did what you were told. The ingredients may not have cared.
Association Is Not Causation, and Yes, We Know
Here's the part where we're supposed to be responsible, and we will be. This study shows an association. It does not prove that these sweeteners damage the brain. Researchers cannot conclude from the data that consuming them directly causes memory loss.
There are real alternative explanations. People who drink lots of diet soda may differ from people who don't in ways a food questionnaire can't capture. Dietary data based on what people remember eating over a year is also inherently squishy. The researchers adjusted for several health factors, but no observational study can adjust for everything.
Still, a 62% faster decline from an amount you'd find in a single can is not a rounding error. It's a flag, planted firmly, in a place where millions of people have been told there was nothing to see.
The Dingo Take
Imagine a pharmaceutical company launched a pill for weight management and a study of 13,000 people found heavy users lost memory and thinking skills 62% faster than everyone else. The pill would be pulled, the CEO would be testifying, and cable news would run a countdown clock. Swap in a can of Diet Coke and we get a shrug and a coupon.
That's the double standard. Sweeteners get treated as food, which means they get the benefit of the doubt, a regulatory process that rarely asks about long-term brain effects, and decades of advertising telling you the zero-calorie version is the grown-up choice. Meanwhile the people most likely to be pushed toward them, those managing diabetes, showed the strongest association with decline. Nobody did that on purpose. But the system built to protect you from this sort of thing mostly waits for the damage to show up in a journal.
Don't panic. Don't pour out your fridge and start narrating your own decline to strangers. This is correlation, and the authors say so plainly. But treat it like the warning light it is. If a study this size finds a signal this size, the food industry owes us better than a shrug and a new flavor launch. Drink some water. Read some labels. And maybe stop letting a billion-dollar marketing budget tell you what counts as healthy.
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