By Danielle 
Sugar substitutes have long been promoted as a healthier alternative to sugar. They don’t cause cavities the way sugar does, and some — like xylitol — may even reduce Streptococcus mutans, the bacteria behind tooth decay. Research has also shown they have little to no impact on blood glucose levels, making them popular for people managing diabetes.
But new evidence suggests the story isn’t all sweet.
A large study published Sept. 3 in Neurology, the medical journal of the American Academy of Neurology, followed 12,772 adults in Brazil over eight years. The participants, who had an average age of 52, were divided into three groups based on how much they consumed low- and no-calorie sweeteners.
Researchers found that six out of seven sweeteners — including aspartame, saccharin, acesulfame-K, erythritol, xylitol and sorbitol — were linked to a 62 per cent faster decline in overall memory and thinking skills compared to the group that consumed the least. Only tagatose showed no association with cognitive decline.
“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 Dr. Claudia Kimie Suemoto of the University of São Paulo.
Related: Study: High sugar-sweetened beverages linked to increased oral cavity cancer risk in women
How the study worked
- Participants filled out detailed diet questionnaires at the start of the study.
- Consumption ranged from an average of 20 milligrams per day in the lowest group to 191 milligrams per day in the highest group.
- For aspartame, that’s roughly the amount in one can of diet soda. Sorbitol had the highest average intake at 64 mg/day.
- Participants completed memory and language tests at the start, middle and end of the study, assessing verbal fluency, word recall, working memory and processing speed.
After adjusting for age, sex, blood pressure and cardiovascular disease, researchers found:
- The highest-consuming group declined 62 per cent faster, the equivalent of 1.6 years of aging.
- The middle group declined 35 per cent faster, or about 1.3 years of aging.
- The link was stronger in participants under age 60 and in people with diabetes.
- No link was found in participants over 60.
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Limits of the findings
The authors noted the study had limitations. Not all artificial sweeteners were included, and diet data was self-reported, which can be unreliable.
“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,” Suemoto said.
The study was supported by the Brazilian Ministry of Health, the Ministry of Science, Technology, and Innovation, and the National Council for Scientific and Technological Development.
Related: German researchers develop calorie-free, much sweeter sugar substitute that doesn’t cause cavities
Related: Obesity and Periodontal Health: What’s the link? Should I be concerned?
What about oral health?
A separate October 2023 systematic review in ScienceDirect examined 977 studies on sugar substitutes and found that sugar alcohols such as xylitol, sorbitol, erythritol and maltitol consistently reduced cavity-causing bacteria in saliva and dental plaque.
These low-intensity sweeteners have long been considered protective for teeth. High-intensity sweeteners, such as aspartame, sucralose, saccharin and stevia, are non-cariogenic — they don’t feed cavity bacteria — but evidence is limited on whether they actively reduce oral bacteria.
One recent study suggested the cavity-preventing effect of aspartame may come mainly from reducing sugar intake, rather than direct antibacterial action.
The bottom line
Sugar substitutes are widely used in “diet” or “sugar-free” products — from soft drinks and baked goods to jams, jellies and dairy.
While they remain better than sugar for teeth and blood glucose, this new study raises concerns that heavy, long-term consumption of most popular sweeteners may accelerate cognitive decline, particularly in people under 60 and those with diabetes.