Study details

For the study, researchers from the University of São Paulo in Brazil tracked 12,772 adults with an average age of 52 for about eight years. Participants were enrolled in the Brazilian Longitudinal Study of Adult Health, which followed nearly 13,000 people between the ages of 35 and 75.

At the start of the study, participants completed detailed questionnaires about their diets over the previous year. Researchers used this information to estimate daily intake of seven low-calorie and zero-calorie sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. 

According to the American Academy of Neurology, these sweeteners are "typically found in ultra-processed foods like flavored water, soda, energy drinks, yogurt and low-calorie desserts."

To analyze the impact on brain health, participants took a battery of cognitive tests three times over the course of the study. These tests measured verbal fluency, working memory, word recall, and processing speed. 

After adjusting for factors such as age, sex, high blood pressure, and cardiovascular disease, researchers found clear differences across consumption groups. The lowest consumers averaged about 20 milligrams of artificial sweeteners per day, while the highest consumed about 191 milligrams — which, for aspartame, is the equivalent to one can of diet soda.

People in the highest tier "showed a 62% faster global cognitive decline than those who consumed the lowest amount — that's the equivalent of 1.6 years of brain aging," said Claudia Kimie Suemoto, associate professor of geriatrics and director of the Biobank for Aging Studies at the University of São Paulo. Participants in the middle tier, who averaged 66 milligrams per day, had a 35% faster decline, roughly equal to 1.3 years of aging. 

The effects were strongest in certain groups. Researchers reported a link in people who were younger — but not older — than 60. They also found that the link to faster cognitive decline was stronger in participants with diabetes.

She also noted that the mechanisms behind these changes are still under investigation. "Animal studies, for example, suggest that aspartame can trigger inflammation in the brain, while sugar alcohols like erythritol and sorbitol may alter gut microbes and compromise the blood-brain barrier," Suemoto said.

Some experts say the study's findings should encourage more scrutiny into sugar substitutes. "The widespread assumption that LNCS (low- and no-calorie sweeteners) represent a safe sugar substitute may be misguided, especially given their ubiquity in products marketed as 'healthier' alternatives," wrote Thomas Holland of Rush University in an editorial accompanying the study. 

But not all scientists are ready to raise alarms. Stanley Hazen, director of the Center for Cardiovascular Diagnostics and Prevention at the Cleveland Clinic Lerner Research Institute, called the study "intriguing and concerning" but also emphasized its limitations, including that "the use of only one diet survey that relied on subject recall, the large and diverse cohort mix and consistency of findings in both diabetics and non-diabetics alike support the reproducibility of the findings."

Given these uncertainties, experts say moderation is key. "It is wise to limit consumption as much as possible, ideally avoiding daily use," Suemoto said. Other guidance highlights broader dietary patterns, such as focusing on a diet that's rich in colorful fruits, leafy greens, nuts, whole grains, and legumes.

For those looking to cut back, small swaps can make a difference. Suggested alternatives include sparkling water instead of diet soda, plain Greek yogurt instead of "light" flavored yogurts, and homemade energy bites instead of sugar-free protein bars.

Industry groups, meanwhile, pushed back strongly. According to The International Sweeteners Association, "sweeteners provide a safe and effective way to reduce sugar and calorie intake, a key public health goal for managing conditions such as obesity and type 2 diabetes."