Swapping sugar for a “zero-calorie” sweetener feels like a healthy choice. It’s the kind of swap many people make without a thought whether to cut calories manage blood sugar or just lighten up their daily coffee.. A large new study published in Neurology, the medical journal of the American Academy of Neurology suggests some of the most common sugar substitutes may not be as harmless for your brain as they seem.All about the studyAs per researchers from the University of São Paulo in Brazil tracked 12,772 adults with an age of 52 for about eight years. Participants completed memory and thinking tests three times during the study measuring fluency, working memory, word recall and processing speed. Alongside this they reported what they ate and drank which let researchers estimate how much of each sweetener they consumed.The findingsThe results were hard to ignore. People who consumed the sweeteners around 191 milligrams per day on average showed a 62 percent faster decline in overall thinking and memory skills compared to those who consumed the least. Researchers estimated this difference was equal to about 1.6 years of brain aging. Even people in the group, who averaged about 66 milligrams daily saw a 35 percent faster decline, roughly equal to 1.3 years of aging.Which sweeteners were involved?Of the seven sweeteners the researchers studied, six were linked to declines in overall thinking, especially memory: aspartame, saccharin, acesulfame K, erythritol, sorbitol, and xylitol. The only one that showed no link was tagatose.Who seemed most affectedInterestingly the connection showed up clearly in adults younger than 60 but wasn’t seen in people older than 60. People with diabetes were also a group of concern. As lead author Dr. Claudia Kimie Suemoto explained the link appeared in middle- people both with and without diabetes but people with diabetes are more likely to use these sweeteners as sugar replacements in the first place.Possible reasons behind the linkThe study itself can’t explain why this might happen. Suemoto pointed to earlier research for possible clues. Animal studies for example suggest aspartame may trigger inflammation in the brain while sugar alcohols like erythritol and sorbitol may change gut bacteria and weaken the blood-brain barrier, the shield that keeps harmful substances out of the brain.An important reality checkBefore anyone panics over their morning coffee it’s important to understand what this study does and doesn’t prove. The researchers were clear that this was a study, which means it found a connection, not a cause. Peoples diets were also self-reported, which can be imperfect, and the study didn’t include every sweetener in use so the results can’t be applied to all sugar substitutes. There’s also a possibility that other factors play a role. Many sugar-free products are processed foods, and Suemoto noted that her own teams earlier research found that eating more ultra-processed foods was linked to faster cognitive decline too.What this means for youThe takeaway isn’t that sweeteners are definitely harming your brain but that “sugar-free” doesn’t automatically mean “risk-free.” As Suemoto put it low-. No-calorie sweeteners are often seen as a healthy alternative to sugar, but certain ones may have negative effects on brain health over time. Larger, longer studies are still needed. In the meantime, paying attention to how much of these sweeteners you consume and treating them as something to moderate rather than ignore seems like a sensible approach.