Adults who ingest daily the amount of artificial sweetener typically found in a can of diet soda exhibited cognitive decline at a rate 62 percent faster than people whose intake is only a fraction of that amount, according to a new eight-year study published in the medical journal Neurology.
Researchers in Brazil followed more than 12,700 adults with an average age of 52 and examined their use of seven common low- and no-calorie sweeteners—aspartame, saccharin, acesulfame K, erythritol, xylitol, sorbitol, and tagatose—found in diet drinks, flavored waters, yogurt, and ultra-processed foods such as breakfast cereals and packaged snacks.
Participants who consumed the most sweeteners averaged 191 milligrams a day, compared with 20 milligrams among those who consumed the least. The research team said the faster rate of cognitive decline among the higher-intake group was equivalent to roughly 1.6 years of additional brain aging.
Six of the seven sugar substitutes studied were associated with faster cognitive decline, particularly memory loss. Tagatose was the lone exception.
“Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar,” said the study’s author, Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil. “However, our findings suggest certain sweeteners may have negative effects on brain health over time.”
The link was strongest among adults younger than 60 and people with diabetes, according to the paper.
Researchers cautioned that the findings are not definitive.
“The results do not show that sweeteners directly cause cognitive decline,” the study said. “They reveal an association, meaning other factors could help explain the pattern.”
The Brazilian findings coincide with last week’s release of a University of Cambridge study that raises new questions about how artificial sweeteners interact with the gut microbiome, the vast community of bacteria and other microorganisms in the digestive system.
In laboratory tests, Cambridge researchers exposed 25 species of gut bacteria to 39 artificial sweeteners. About three-quarters of the sweeteners altered at least one species, with some slowing or stopping microbes associated with digestive health and blood-sugar regulation.
Researchers also looked at how sweeteners interacted with caffeine, flavorings, and medications, identifying more than 100 instances in which those substances amplified or reduced the sweeteners’ effect on gut bacteria.
One of the strongest interactions involved isosteviol, a low-calorie sweetener used by the food and beverage industry. When combined with the antidepressant duloxetine, it significantly suppressed two beneficial gut microbes linked to digestive health, blood-sugar regulation, and immune function.
“Sweeteners are often marketed as metabolically neutral, but our study challenges this idea,” said Dr. Sonja Blasche, a lead author of the Cambridge study.
Professor Kiran Patil of the university’s Medical Research Council Toxicology Unit said the findings underscore how much remains unknown about sweeteners’ impact on human health.
“Our study suggests that artificial sweeteners don’t just pass through the body passively—they can interact with gut microbes, and these effects can be amplified or altered by other substances like medications,” said Patil, the study’s senior author. “These findings can help guide new studies toward understanding how sweeteners might influence health in unexpected ways.”
The authors of both studies said additional research is needed before scientists can establish firm links between artificial sweeteners and cognitive decline, changes in the gut microbiome, or other physiological effects.
Still, the findings add to a growing body of research examining whether products marketed as healthier alternatives to sugar may have unintended consequences.
—Kevin Haynes
This article originally appeared on Fast Company’s sister website, Inc.com.
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