For millions of Americans, a diet soda is an easy everyday indulgence: cold, bubbly and sweet, but without the sugar and calories found in regular soft drinks.
New research, however, is raising fresh questions about whether some zero-calorie beverages may come with a hidden cost for the brain.
A team of researchers in Brazil focused on aspartame, the widely used artificial sweetener that is roughly 200 times sweeter than table sugar and commonly appears in diet sodas, sugar-free desserts and other low-calorie products.
After analyzing data from nearly 13,000 adults, the researchers found that people who consumed an amount of aspartame roughly equivalent to what is in one can of diet soda showed an additional 1.6 years of cognitive aging compared with those who consumed very little.
The association was not limited to the highest consumers. Participants who took in less than a can’s worth of aspartame still appeared to have an extra 1.3 years of brain aging.
On cognitive testing, that group also experienced a decline in thinking and memory skills that was more than 60 percent faster, a finding the researchers described as a “clear difference” between the highest and lowest aspartame consumers.
Cognitive aging occurs as key brain structures gradually deteriorate, including shrinkage in areas such as the frontal cortex and damage to the protective myelin that surrounds nerve cells. Over time, those changes can slow mental processing and weaken memory, both hallmarks of cognitive decline.
Still, the authors urged caution, noting that the study does not prove aspartame directly causes cognitive decline. They also emphasized that other health factors, including diabetes, may play a role in the increased risk observed among participants.
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But it does raise concerns about zero-calorie sweeteners that are generally considered healthier than regular sugar.
‘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,’ Dr Claudia Kimie Suemoto, study author from the University of São Paulo in Brazil, said.
The study, published in the journal Neurology, researchers followed 12,772 adults with an average age of 52 for about eight years.
At the beginning, they filled out detailed questionnaires about their food and drink consumption over the past year. Researchers then placed them into three groups based on their total sweetener intake.
Sweeteners included were aspartame, saccharin, acesulfame K, erythritol, xylitol, sorbitol and tagatose.
The lowest group averaged 20mg a day, while the highest had 191mg daily, about the amount of aspartame in a can of diet soda.
Participants also completed cognitive assessments at the beginning, middle and endpoint of the study. These evaluated verbal skills, working memory, word recall and processing speed.
After accounting for age, sex and chronic conditions like high blood pressure and heart disease, the researchers found people who consumed the greatest amount of sweeteners experienced a 62 percent faster decline in cognitive skills and 1.6 added years of brain aging.
Those in the middle group had a 35 percent faster decline and 1.3 extra years of brain aging.
However, age seemed to influence the results, as among those under 60, those who consumed the most sweeteners had faster drops in verbal fluency and overall cognitive performance than those who consumed the least.
People over 60 did not demonstrate the same association.
Additionally, diabetes was associated with faster decline, which may be because the condition can damage blood vessels in the brain.
Tagatose was the only sweetener in the study not associated with cognitive decline.
‘While we found links to cognitive decline for middle-aged people both with and without diabetes, people with diabetes are more likely to use artificial sweeteners as sugar substitutes,’ Suemoto said.
‘More research is needed to confirm our findings and to investigate if other refined sugar alternatives, such as applesauce, honey, maple syrup or coconut sugar, may be effective alternatives.’
