Not so sweet: Some sugar substitutes linked to faster cognitive decline, reveals research

Some sugar substitutes may come with unexpected consequences for long-term brain health, according to a study published in the September 3, 2025, issue of Neurology, the medical journal of the American Academy of Neurology. The study examined seven low- and no-calorie sweeteners and found that people who consumed the highest amounts experienced faster declines in thinking and memory skills compared to those who consumed the lowest amounts. The link was even stronger in people with diabetes. While the study showed a link between the use of some artificial sweeteners and cognitive decline, it did not prove that they were a cause.

The artificial sweeteners examined in the study were aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose. These are mainly found in ultra-processed foods like flavored water, soda, energy drinks, yogurt and low-calorie desserts. Some are also used as a standalone sweetener.

“Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar, however our findings suggest certain sweeteners may have negative effects on brain health over time,” said study author Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil.

The study included 12,772 adults from across Brazil. The average age was 52, and participants were followed for an average of eight years.

Participants completed questionnaires about diet at the start of the study, detailing what they ate and drank over the past year. Researchers divided them into three groups based on the total amount of artificial sweeteners they consumed. The lowest group consumed an average of 20 milligrams per day (mg/day) and the highest group consumed an average of 191 mg/day. For aspartame, this amount is equivalent to one can of diet soda. Sorbitol had the highest consumption, with an average of 64 mg/day.

Participants were given cognitive tests at the start, middle and end of the study to track memory, language and thinking skills over time. The tests assessed areas such as 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 people who consumed the highest amount of sweeteners showed faster declines in overall thinking and memory skills than those who consumed the lowest amount, with a decline that was 62% faster. This is the equivalent of about 1.6 years of aging. Those in the middle group had a decline that was 35% faster than the lowest group, equivalent to about 1.3 years of aging.

When researchers broke the results down by age, they found that people under the age of 60 who consumed the highest amounts of sweeteners showed faster declines in verbal fluency and overall cognition when compared to those who consumed the lowest amounts. They did not find links in people over 60. They also found that the link to faster cognitive decline was stronger in participants with diabetes than in those without diabetes.

When looking at individual sweeteners, consuming aspartame, saccharin, acesulfame-k, erythritol, sorbitol and xylitol was associated with a faster decline in overall cognition, particularly in memory.

They found no link between the consumption of tagatose and cognitive decline.

“While we found links to cognitive decline for middle-aged people both with and without diabetes, people with diabetes are more likely to use artificial sweeteners as sugar substitutes,” Suemoto said. “More research is needed to confirm our findings and to investigate if other refined sugar alternatives, such as applesauce, honey, maple syrup or coconut sugar, may be effective alternatives.”

A limitation of the study was that not all artificial sweeteners were included. Also, diet information was reported by the participants, who may not have remembered accurately everything they ate.

Reference:

Claudia Kimie Suemoto, Association Between Consumption of Low- and No-Calorie Artificial Sweeteners and Cognitive Decline, An 8-Year Prospective Study, Neurology, https://doi.org/10.1212/WNL.0000000000214023