“Sugar-free” can seem smart. A diet soda at lunch, a low-calorie yogurt after school, a packet in your coffee, and it all seems harmless.
A long-term study that followed 12,772 adults in Brazil, published in the journal of the American Academy of Neurology, found that heavier intake of common low- and no-calorie sweeteners, often called artificial sweeteners, was linked to a faster decline in memory and other thinking skills.
The biggest differences showed up in adults younger than 60 and in people with diabetes, and the researchers emphasized that the data show a link, not cause and effect.
The work was supported by the Brazilian Ministry of Health, the Ministry of Science, Technology, and Innovation, and the National Council for Scientific and Technological Development.
Where these sweeteners show up
Low- and no-calorie sweeteners are ingredients that make foods taste sweet with few or no calories. They show up across “diet,” “light,” and “zero” products, and sometimes in places people do not expect.
Many of the biggest sources are ultra-processed foods and drinks. That term usually refers to packaged products made with industrial ingredients and additives, not just food that was cooked and stored.
In everyday life, that can mean flavored waters, sodas, energy drinks, yogurt, and low-calorie desserts. It can also mean sweeteners sold on their own for coffee, tea, and baking.
How the study followed people
Researchers tracked participants for about eight years, with cognitive testing at multiple points along the way. The tests measured skills like word finding, short-term memory, recalling words later, and how quickly people process information.
Diet was captured with detailed questionnaires at the start of the study, covering what participants ate and drank over the prior year. That method is common in nutrition research, but it relies on self-reporting, so it can miss details.
The paper’s first author was Natalia Gomes Gonçalves, and the senior author was Claudia Kimie Suemoto of the University of São Paulo. Their team focused on midlife because subtle brain changes can start years before anyone notices them.
She said “low- and no-calorie sweeteners are often seen as a healthy alternative to sugar,” but added that the findings suggest “certain sweeteners may have negative effects on brain health over time.”
The steepest decline showed up in the highest users
To estimate exposure, the researchers totaled sweetener intake from all sources and then grouped people by how much they consumed. The lowest-intake group averaged about 20 milligrams per day, while the highest-intake group averaged about 191 milligrams per day, roughly the amount of aspartame in a can of diet soda.
Over the follow-up, the highest-intake group declined 62 percent faster in overall thinking and memory than the lowest-intake group. People in the middle-intake group also declined faster, at a rate 35 percent higher than the lowest group.
The team translated that gap into something most readers can picture. The difference between the highest and lowest groups was similar to about 1.6 extra years of aging, while the middle group was closer to about 1.3 years.
Why age and diabetes mattered so much
When researchers analyzed age, the association was clearer among participants younger than 60. In that group, higher sweetener intake tracked with steeper drops in verbal fluency and overall cognitive scores.
Among adults older than 60, the study did not find a significant association. That does not mean there is no risk, but it suggests the relationship may depend on timing in life or other health factors.
The link was also stronger in participants with diabetes than in those without it. That matters because many people with diabetes use sweeteners as a long-term substitute, not as an occasional choice.
Most sweeteners were linked, one was not
The study examined seven sweeteners commonly used in foods and drinks. They were aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose.
Higher intake of aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol was linked to faster cognitive decline, especially in memory. Sorbitol had the highest average intake among the sweeteners, at about 64 milligrams per day.
Tagatose was the exception, with no observed association in this analysis. It is a reminder that “artificial sweetener” is a broad label, and different ingredients may not behave the same way in the body.
Limits and unanswered questions
Because this was an observational study, the researchers could not prove that sweeteners themselves caused the changes in test scores. Sweeteners are also often consumed in ultra-processed foods, which can come with other ingredients and lifestyle factors that are hard to fully separate.
Diet information was self-reported and collected once at the beginning, so it cannot capture every change in eating habits over eight years. A university news report on the study also noted that the analysis did not include every sweetener on the market, including sucralose, which is widely used today.
So what comes next? Researchers will likely want studies that track diet changes over time, measure sweetener exposure more precisely, and test possible biological pathways instead of relying only on questionnaires.
How experts and industry are reacting
The conversation is already turning into a debate about messaging. In a post responding to an industry critique, the researchers said the phrase “Not so sweet” came from an independent editorial in the same journal issue, written by Thomas Monroe Holland of Rush University, not from the research paper’s title.
Industry groups are pushing back on strong conclusions. The International Sweeteners Association urged careful interpretation, emphasizing that observational studies can be influenced by overall diet and lifestyle and that safety reviews consider the total body of evidence.
For readers, the take-home point is not a panic moment. It is a signal that “zero sugar” is not automatically a free pass, especially for heavy users, and that brain health may need to be part of the nutrition conversation.
The main study was published in Neurology.
