Adults who consume roughly the amount of artificial sweetener found in a single can of diet soda every day showed cognitive decline 62% faster than those who consumed nearly none. A large study in Brazil tracked 12,772 adults with an average age of 52 over eight years and found the difference equal to 1.6 extra years of brain aging.
One can’s worth of sweetener, eight years of data
Dr. Claudia Kimie Suemoto at the University of São Paulo led the research. Her team measured cognitive changes through tests of verbal fluency, working memory, word recall, and processing speed—areas that often decline early in neurodegenerative diseases. Participants were grouped by sweetener intake: the lowest averaged 20 milligrams daily, while the highest averaged 191 milligrams, about the amount in a single diet soda.
Those consuming around 66 milligrams per day declined 35% faster than the lowest group, equal to 1.3 additional years of aging. After adjusting for age, sex, blood pressure, and cardiovascular disease, the highest intake group showed the 62% faster decline. Six of the seven sweeteners studied—aspartame, saccharin, acesulfame K, erythritol, sorbitol, and xylitol—were tied to faster decline. Only tagatose showed no link.
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Age and diabetes amplify the risk
The effects varied by age. Adults under 60 experienced noticeable decline, while those over 60 showed almost none. Suemoto described the age pattern as unexpected and suggested older adults’ already variable cognitive trajectories might hide sweetener-related changes. Dr. Andrew Budson, a Harvard neurology lecturer, pointed out the challenge of isolating sweetener effects amid broader aging processes.
People with diabetes, who often use sweeteners as sugar substitutes, faced stronger associations. Suemoto noted that while links appeared for middle-aged individuals both with and without diabetes, those with the condition are more likely to consume artificial sweeteners. The study did not advise giving up sweeteners but suggested exploring alternatives like applesauce, honey, or maple syrup.
The results match a separate Cambridge University study published in Molecular Systems Biology. That research found many sweeteners disrupt gut bacteria, and these effects worsen when combined with common medications. The team tested 39 sweeteners against gut bacterial species, then paired them with prescription drugs, caffeine, and food flavorings. About three-quarters of the sweeteners altered at least one bacterial species, and combinations showed amplified or diminished effects.
The most concerning interaction involved stevia-derived compounds and a widely used antidepressant. The findings come from lab cultures, not human trials, and the researchers emphasized that real-world gut complexity can’t be fully replicated in a dish.
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Natural doesn’t mean safe
The Cambridge study challenges the idea that “natural” sweeteners like stevia or monk fruit are inherently safer. Overall, three-quarters of the 39 sweeteners tested—both synthetic and natural—altered gut bacteria. The “natural versus artificial” distinction did not predict safety in drug combinations.
The International Sweeteners Association responded by noting the observational nature of the Neurology study, which cannot prove causation. Other factors like diet, lifestyle, and underlying health conditions could influence both sweetener use and cognitive decline. Reverse causality is also possible: people with metabolic conditions may consume more sweeteners while already being at higher risk for cognitive issues.
Critics also pointed out the study’s broad categorization of sweeteners. Aspartame, a synthetic compound metabolized into amino acids, and erythritol, a sugar alcohol that enters the bloodstream largely unchanged, have different biochemical profiles. Grouping them together may obscure which compounds pose the greatest risk—and for whom.
Erythritol has faced separate scrutiny. A 2023 study in Nature Medicine linked high erythritol blood levels to more than double the risk of heart attack, stroke, or death over three years. The mechanism—platelet activation and clot formation—differs from the cognitive decline pathway studied in Brazil. Switching from aspartame to erythritol doesn’t remove risk; it replaces one concern with another.
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The 62% faster decline reflects a quicker drop in verbal fluency, working memory, word recall, and processing speed—not dementia. The researchers estimated the difference as equal to 1.6 extra years of aging. The effect appeared at typical consumption levels: the highest intake group averaged 191 milligrams daily, about one diet soda. The middle group, at 66 milligrams, still showed a 35% faster decline.
Neither study recommended immediate dietary changes. The Brazilian research is observational, and the Cambridge findings come from lab cultures. Both teams called for human trials to confirm the mechanisms. The studies collectively question the assumption that sweeteners are biologically neutral. The World Health Organization reached a similar conclusion in 2023, advising against sweeteners for weight management.
For people with diabetes, who showed the strongest cognitive associations, discussing sweetener use with a doctor may be wise. For others, the message was straightforward: more research is needed. The claim that sweeteners are metabolically inert is no longer credible.