Many people turn to low- and no-calorie sweeteners as a healthier option to cut down on sugar.
These artificial sweeteners are often found in diet sodas, flavored water, energy drinks, yogurt, and sugar-free desserts.
But a new study suggests that using some of these sugar substitutes may have an unexpected downside — they could be bad for your brain over time.
The study, published in the September 3, 2025, issue of Neurology®, followed over 12,000 adults across Brazil for an average of eight years.
It found that people who consumed the most artificial sweeteners experienced faster declines in memory, thinking, and language skills than those who consumed the least. The effect was even stronger in people with diabetes.
The researchers looked at seven common sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. These sweeteners are common in ultra-processed foods and some are also sold as sugar substitutes on their own. Among them, sorbitol had the highest daily intake on average.
Participants answered detailed questions about their diet, including what they ate and drank over the previous year. They were divided into three groups based on how much sweetener they consumed. The group with the highest intake consumed about 191 milligrams per day, while the lowest group consumed just 20 milligrams.
To measure brain function, participants completed memory and thinking tests at the beginning, middle, and end of the study. These tests evaluated verbal fluency, working memory, processing speed, and word recall.
After adjusting for health factors like age, blood pressure, and heart disease, the researchers found that the highest sweetener consumers had a 62% faster decline in thinking and memory abilities. This is roughly equal to aging the brain by 1.6 years. The middle group had a 35% faster decline — about 1.3 years of extra aging.
Interestingly, the link was stronger in people under 60. Those under 60 who consumed the most sweeteners had steeper drops in verbal fluency and overall thinking skills. The link was also stronger for people with diabetes, who often use sweeteners as a sugar substitute.
When the researchers examined individual sweeteners, most of them — including aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol — were linked to memory and cognitive decline. Tagatose, however, was not associated with any decline.
Dr. Claudia Kimie Suemoto, one of the study authors, said that although sweeteners are often considered safe alternatives to sugar, these findings raise concerns about their long-term effects on brain health. She emphasized the need for more research, especially on natural alternatives like applesauce, honey, or coconut sugar.
It’s important to note that the study doesn’t prove sweeteners cause memory loss — it only shows a link. Also, diet information was self-reported, which may affect accuracy. Not all sweeteners were included in the study.
Still, these results support growing concerns about the overuse of ultra-processed foods and artificial ingredients. They suggest we may need to be more careful when choosing sugar substitutes, especially if brain health is a concern.
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The study is published in Neurology.
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