What the study measured
Researchers followed 12,772 adults in Brazil for about eight years, starting when participants were 52 years old on average. At the beginning, each person filled in a detailed diet questionnaire covering the previous year, which the team used to estimate daily intake of seven sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose.
Those in the highest intake group showed a 62 percent faster decline in memory and thinking skills than those in the lowest, the equivalent of about 1.6 additional years of brain aging. Six of the seven sweeteners were linked to faster decline.
The results appear in Neurology, the journal of the American Academy of Neurology.
Stronger signal in people with diabetes
The association was most pronounced among participants with diabetes, a group that already carries a higher risk of cognitive problems and often uses these products heavily.
"Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar; however, our findings suggest certain sweeteners may have negative effects on brain health over time," said study author Claudia Kimie Suemoto of the University of São Paulo.
What it does not prove
The authors are explicit that the study shows an association, not cause and effect. People who consume more diet drinks may differ from those who do not in ways a questionnaire cannot capture, and the paper cannot rule out that early cognitive changes altered eating habits rather than the reverse.
There are limits on how far the numbers travel. Participants came from one country, and diet was recorded once, covering a single year, rather than tracked as habits changed.
The practical reading is modest. The finding adds to a growing body of work questioning whether swapping sugar for sweeteners is a free trade for long-term health, and it gives clinicians one more reason to ask what patients drink. It does not mean an occasional diet soda damages the brain.