A new study reveals the risk of sweeteners to brain health

By Ananya Dash

Sweeteners may not be the wonder substitute for sugars that they have always been hoped to be. While they make everything taste sweet without piling up calories, they aren’t without side effects. A study published in Neurology in September 2025 adds to the growing body of research that shows dependence on sweeteners, as an alternative to sugars, has long-term negative health effects.

“We found that people with high consumption of sweeteners have a cognitive decline that is more than expected of their age than the people who do not use sweeteners or use a very small amount,” said Claudia Kimie Suemoto, a geriatrician and physician at the University of São Paulo, Brazil and the lead author of the study.

The source of sweeteners varies: They can come from plants, be made from molecules in nature, or be invented in labs. For the study, Suemoto’s team studied seven sweeteners at once—three invented and four made from molecules in nature—in 12,000 participants. The highest tier of sweetener lovers consumed an amount of sweetener equal to one to four cans of diet soda per day. Those in the lowest tier consumed very little or no sweeteners at all.

The participants recalled their food choices at three time points in an eight-year time window. At those time points, authors asked participants to visit a laboratory to evaluate their brain function with standardized tests.

The authors found that the cognitive decline in top sweetener lovers was roughly equal to one and half years of extra brain aging and was only true for people younger than 60, not older. “Midlife is when the biological framework for dementia is often laid, even decades before memory symptoms appear,” said Thomas Holland, physician-scientist and assistant professor at the Rush Institute for Healthy Aging, who was not involved in the study. “The stronger associations seen in adults under 60 reinforce that prevention should begin early.”

Evidence over the last decade has shown that sweeteners lead to worse health outcomes for brain health. A U.S.-based study published in 2017 had 1,500 participants in their sixties and showed a three-fold increase in risk for dementia for people who consumed drinks containing artificial sweeteners. Suemoto’s previous work, published in 2023, also showed that ultra-processed foods, which tend to be rich in sweeteners, accelerate brain aging. Suemoto’s new study builds on the existing evidence by including both food and drinks and by studying multiple sweeteners at once. Also, because the authors conducted their research in a racially diverse Brazilian population, their findings are broadly applicable.

The study also revealed that brain aging was worse in sweetener lovers who were diabetic. Holland says that people with diabetes are primed for nerve damage and consuming sweeteners causes even more damage to their brains. He uses this finding to emphasize that brain health is a culmination of our lived experiences. Having diabetes and consuming sweeteners risks brain aging as much as living a sedentary lifestyle or lacking access to green spaces. Diabetes is just one powerful example to understand this effect.

But there’s a downside to observational studies such as Suemoto’s: They only measure a slice of participants’ lives. The study’s protocol may not detect other influences. “People can choose to eat one thing over other because they may already have some health issues, or they can have health conditions that authors aren’t testing for,” said Mary Scourboutakos, a physician and nutrition expert at Eastern Virginia Medical School, who was not involved in the study. “Sometimes (observational studies) are the best research that we have, because it is really hard to enroll people, put them on a diet, and keep them on it for years.”

A definitive consensus on whether the findings hold true is hard to achieve, as they do not directly measure how sweeteners cause brain aging. Still, the study’s results are consistent with pre-existing research that shows a similar link between sweeteners and brain health, despite being done in different populations.

Decades of research show that sugars are clearly harmful, given that they increase the risk of obesity, diabetes, cardiovascular diseases, and dementia. But sweeteners are not the safest substitute. “The key is moderation and a gradual shift away from constant exposure to sweet flavors,” Holland said.