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One diet soda a day – about 191 mg of artificial sweetener – was enough to put adults under 60 on a steeper cognitive slope than those who consumed almost none. That specific number comes from a 2025 study published in Neurology, the journal of the American Academy of Neurology, and it’s the kind of finding that stops you mid-sip.
The study didn’t examine exotic compounds. It looked at sweeteners most people encounter daily: aspartame in diet sodas, saccharin in some table-top sweetener packets, acesulfame-K in energy drinks, and sugar alcohols like erythritol, sorbitol, and xylitol hiding in everything from protein bars to flavored yogurts. These are the ingredients on the back of countless products sold with words like “sugar-free,” “light,” and “better for you” on the front.
The question researchers set out to answer wasn’t whether these sweeteners caused weight gain or blood sugar problems – that debate has been running for decades. The question was simpler and, as it turns out, more alarming: what are they doing to the brain over time?
The Study Behind the Finding
The research followed 12,772 adults participating in the Brazilian Longitudinal Study of Adult Health, who underwent standard cognitive tests every four years across three study waves spanning 2008 to 2019. It is the largest and longest prospective study to date investigating the association between artificial sweetener consumption and cognitive decline.
Researchers tracked participants with an average age of 52, estimating their consumption of seven artificial sweeteners from food frequency questionnaires completed at the study’s start. Participants also underwent cognitive tests at the start, middle, and end of the study to track memory, language, and thinking skills. The six assessments covered a range of mental abilities, including verbal fluency – the capacity to retrieve and generate words from memory quickly, a skill that tends to flag cognitive problems early.
The intake range between groups was relatively modest. Participants under age 60 who consumed the largest total amounts of artificial sweeteners showed 62% faster declines in thinking and memory skills compared to those who consumed the lowest amounts. That faster decline equaled about 1.6 years of aging. The lowest intake group averaged around 20 mg per day. The highest averaged roughly 191 mg – equivalent to the aspartame content of one can of diet soda, according to the research team.
Even the middle ground showed measurable effects. People who consumed moderate amounts of sugar substitutes had brain decline 35% faster than the lowest group, equivalent to about 1.3 years of additional aging.
Which Sweeteners Were Involved
Aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol were all individually associated with faster decline in overall cognition, particularly memory. Only tagatose could not be linked with cognitive decline.
The composition of that list matters. These are not obscure additives. They are mainly found in ultra-processed foods like flavored water, soda, energy drinks, yogurt, and low-calorie desserts. The FDA has approved six high-intensity sweeteners as food additives in the United States: saccharin, aspartame, acesulfame-K, sucralose, neotame, and advantame.
Sorbitol deserves a specific mention because it’s easy to overlook. It’s commonly found in sugar-free gums, mints, and some dried fruits – products most people wouldn’t think twice about. A food frequency questionnaire was used to calculate combined and individual consumption of the sweeteners, including sugar alcohols erythritol, sorbitol, and xylitol. Among the group, sorbitol had the highest mean daily consumption of all sweeteners studied, at 64 mg per day, according to the Neurology data.
The Under-60 Effect
One of the more striking patterns in the findings involves age. When researchers analyzed the results by age, people under 60 who consumed the highest amounts of sweeteners showed faster declines in verbal fluency and overall cognition – a finding that did not apply to those over 60.
As Dr. Thomas Holland, an instructor at Rush University’s Institute for Healthy Aging in Chicago, wrote in an accompanying editorial published in Neurology: “This suggests that midlife dietary exposures, decades before cognitive symptoms emerge, may carry life-long consequences for brain health.”
That observation reframes the risk entirely. Older adults may simply have already passed a window when dietary exposure does its formative work. The brain changes that eventually manifest as memory loss or cognitive slowing in later life may be shaped by what people eat in their 40s and 50s.
The link was even stronger in people with diabetes – a population that often relies most heavily on these sweeteners as sugar substitutes. “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,” noted Claudia Kimie Suemoto, MD, PhD, associate professor of geriatrics at the University of São Paulo and lead author of the study.
Why the Brain May Be Affected
The study didn’t establish a direct cause – it was observational, meaning it tracked associations rather than proving a mechanism. The study showed a link between the use of some artificial sweeteners and cognitive decline, but did not prove that they were a cause.
Still, researchers have proposed plausible pathways. The research team suspects artificial sweeteners may influence the brain through neuroinflammation, neurodegeneration, or disruption of the gut-brain axis. “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.
The gut-brain connection – the signaling pathway between your digestive system and your brain – is increasingly central to cognitive health research. Accumulating evidence shows that non-caloric sweeteners interact with host physiology, altering gut microbiota composition and neural circuits that regulate feeding, according to a 2025 review in the International Journal of Molecular Sciences. Disrupting gut bacteria changes the chemical signals the brain receives, and the consequences may extend well beyond digestion.
Animal studies used very large doses, well beyond what most people consume daily, so those results probably don’t translate directly to typical intake levels – “more research is needed both in animal models and mostly in humans,” Suemoto noted.
This distinction between observational association and proven cause-and-effect is real and worth keeping. The study cannot say that eliminating these sweeteners will reverse or prevent cognitive decline. It can say that higher intake was consistently linked to faster cognitive slippage in a large cohort tracked across eight years.
The verbal fluency numbers are worth a closer look, too. The link was found in people younger than 60 years but not in older adults and was stronger in people with diabetes. Verbal fluency – the ability to quickly retrieve words from memory – is one of the earliest cognitive abilities to show measurable decline and is used clinically to detect early cognitive impairment. Declines here often precede broader memory problems by years.
It’s also worth noting what the study could not fully assess. Not all artificial sweeteners were included, and diet information was self-reported by participants, who may not have remembered accurately everything they ate. That’s a standard limitation of dietary research – people consistently underestimate or misremember intake – and it may mean the actual exposure differences between groups were even larger than measured.
For readers interested in how other dietary patterns connect to brain aging, research on ultra-processed foods and their effects on the brain and body shows a consistent theme: regular consumption of industrially processed products is linked to measurable changes in multiple organ systems, including the brain.
What to Do With This Information
The study’s lead author didn’t advise panic. 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.”
That’s a reasonable and honest position. One observational study – even a large, well-designed one – doesn’t overturn dietary guidance overnight. But the findings do add to a growing pile of evidence that low- and no-calorie sweeteners may not be the consequence-free swap they were marketed as. The assumption that zero calories meant zero risk is proving harder to sustain.
What to Do Now
The practical starting point is awareness. Many “healthy” products carry multiple sweeteners simultaneously – a flavored yogurt might contain erythritol and acesulfame-K, a protein bar might combine sorbitol and aspartame. Reading ingredient lists rather than relying on front-of-pack claims is the first concrete step. The total daily intake can add up faster than it appears.
The study’s findings were concentrated in people consuming around 191 mg daily – the equivalent of one diet soda. That’s not an extreme amount. It’s a daily habit that millions of people maintain without a second thought, often in the belief that they’re making a healthier choice than regular soda.
For people with diabetes who rely on these sweeteners as part of blood sugar management, the findings are worth discussing with a doctor rather than acting on unilaterally. The risk-benefit calculation is more complex in that group, and eliminating sweeteners without replacing them thoughtfully could create different problems.
For everyone else, the evidence points toward reducing routine reliance on sweetened low-calorie products rather than treating occasional use as a concern. Whole fruit delivers sweetness alongside fiber, antioxidants, and micronutrients. A small amount of honey or maple syrup, used intentionally, contributes far less daily sweetener load than someone who habitually drinks diet sodas or snacks on sugar-free products throughout the day. The goal isn’t perfection – it’s reducing the drip of daily exposure that the research suggests may, over years, matter more than any single dietary decision.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here. AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
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