Sugar substitutes are marketed as a healthier alternative to regular sugar, stand-ins that will offer the same sweet taste but won’t pose the same threat to your weight or dental health. Sounds like a win-win, right? Well, not so fast. Newer research suggests there might be a catch (or several).
In a study published in the scientific journal Neurology in fall 2025, researchers found that consuming higher amounts of several common sugar substitutes was linked to accelerated cognitive decline in Brazilian adults. While sugar substitutes can definitely have health benefits compared to regular sugar, Christine Byrne, MPH, RD, a dietitian and the owner of Ruby Oak Nutrition in Raleigh, North Carolina, tells SELF, “this is yet another example that proves nutrition is complicated, and many food choices come with pros and cons.”
“Choosing artificial sweetener instead of sugar can help with blood sugar control and reduce your consumption of added sugar, too much of which can have negative health impacts,” she adds. “But it may come with downsides, like this potential for cognitive decline.”
What the study found
The Neurology researchers examined seven common sugar substitutes specifically: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. To analyze their combined and individual effects on cognitive function, the researchers followed 12,772 adults hailing from all over Brazil for around eight years and tested their cognitive function at the beginning, middle, and end. Participants had an average age of 52 years old, were 55% women, and were 43% Black or mixed race.
At the outset, the researchers were able to determine participants’ sugar substitute intake through a detailed questionnaire asking about what they ate and drank in the previous 12 months. Then, the researchers classified participants based on their intake: low (an average of 20 milligrams [mg] of sugar substitutes per day), medium (an average of 66 mg per day), and high (an average of 191 mg per day).
When the researchers adjusted the data for potential confounding factors, like age, sex, race/ethnicity, education, physical activity, BMI, high blood pressure, and cardiovascular disease, they found that participants with the highest combined sugar substitute intake (which we’ll call the “highest-intake category” here) had declined 62% faster in overall cognitive function than the lowest-intake category—a difference roughly comparable to 1.6 years of aging. Similarly, the middle-intake category had also declined faster, by 35%—akin to 1.3 years of aging. Both the highest-intake category and the middle-intake category had also seen drops in specific cognitive areas, including memory (by 32% for the highest-intake category) and verbal fluency (by 110% for the middle-intake category and 173% for the highest-intake category).
This trend was only apparent in participants under 60 years old, and was especially strong in participants with diabetes.
When the researchers looked closer at the individual sugar substitutes, they found that higher intake of six of the seven—aspartame, saccharin, acesulfame-k, erythritol (the least consumed), sorbitol (the most consumed), and xylitol—was also tied to faster cognitive declines, particularly memory and verbal fluency. Tagatose was the only exception.
What this means for you
Ultimately, this study suggests that consuming sugar substitutes over an extended period of time is associated with worse cognitive health. Importantly, this association doesn’t necessarily signify that sugar substitutes cause cognitive decline. Rather, it means the two variables are correlated. “It doesn’t mean the study is irrelevant, but it’s an important distinction,” Byrne says.
Hypothesizing a possible explanation for the link between higher sugar substitute intake and accelerated cognitive decline, the researchers posited that sugar substitutes might produce toxic metabolites during digestion, which, in turn, have a damaging effect. Basically, the authors are saying this link “could be because these sweeteners get broken down into other compounds in the body, and those compounds may cause inflammation in the brain,” Byrne explains. Fundamentally, she notes, “the thing about studies like this one, that look at correlations between certain behaviors (in this case, consuming artificial sweeteners) and certain health outcomes, is that it’s impossible to know what the mechanism is.”
What’s more, the study isn’t the first to raise the alarm regarding the impact of sugar substitutes on cognitive function. Previous studies have also found links between both artificially sweetened products (like soft drinks) and individual sugar substitutes (like sucralose and saccharin) and cognitive issues, including reduced memory and executive function and increased dementia risk.
With all this said, these findings don’t mean that sugar substitutes are bad for you across the board, or that you should try to cut them out entirely. Besides, that would be tough, or even impossible to do, considering how prevalent they are in food and drink products, particularly low-calorie ultraprocessed items like soda, light yogurt, flavored water, and energy drinks. Three of the seven sugar substitutes involved in the study—erythritol, sorbitol, and xylitol—belong to a category known as sugar alcohols, artificial sweeteners that can be found in sweet treats like candy, ice cream, baked goods, and protein bars (and can cause digestive symptoms), for example.
“If someone is drinking several diet sodas or other artificially sweetened things per day, they might take this as a sign to cut back,” Byrne says. “But I don’t think this is a reason for everyone to panic and swear off artificial sweeteners completely if they enjoy them on occasion.”
Related:
- 5 Everyday Behaviors That Neurologists Avoid for Long-Term Brain Health
- The One Habit a Neurologist Does Every Day to Protect Her Brain Long-Term
- 6 Habits Neurologists Swear By to Keep Their Brains Sharp
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