Sugar is one of the main villains in our diets. It’s hidden in all sorts of products, from sauces to fizzy drinks, and we consume too much of it. Sugar-free sweeteners seem like the smarter, healthier choice. They probably are. But they’re not without their own problems.
A new study that followed nearly 13,000 adults for almost a decade found that some of the most common artificial sweeteners are linked to accelerated cognitive decline. In other words, people who eat more artificial sweeteners seem to have faster-aging brains.
Sugar on the Brain
A team of researchers led by Dr. Claudia Kimie Suemoto at the University of São Paulo in Brazil analyzed data from the Brazilian Longitudinal Study of Adult Health, a massive project tracking the well-being of civil servants. They looked at the diets of 12,772 participants, who had an average age of 52 at the study’s start. Using detailed food frequency questionnaires, the scientists calculated how much of seven specific low- and no-calorie sweeteners (LNCSs) each person consumed. They looked at a broad range of sugar substitutes, including aspartame, saccharin, acesulfame-K, and the sugar alcohols erythritol, xylitol, and sorbitol.
Participants were then put through a battery of cognitive tests at three different points over the eight-year follow-up period. These were tests designed to measure the brain’s core executive functions: memory (how well you recall words), verbal fluency (how quickly you can summon words), and processing speed (how fast you can think on your feet). The sum of these abilities is often referred to as “global cognition” — a snapshot of your overall mental sharpness.
The results were startling. The researchers divided the participants into three groups based on their sweetener intake. The lowest group consumed very little, an average of 20 milligrams per day. The highest group, however, consumed nearly ten times that amount, averaging 191 milligrams a day. To put that in perspective, a single 12-ounce can of diet soda contains roughly 180-200 milligrams of aspartame. So, we’re talking about a one-a-day habit.
Sweet Misery
After adjusting for a host of other factors that could influence brain health (like age, sex, education level, high blood pressure, and a history of heart disease, the pattern was clear and dose-dependent. Compared to the lowest consumers, the middle group’s cognitive skills declined 35% faster. But for the group consuming the most sweeteners, the decline was a striking 62% faster.
The scientists translated this into a more chilling metric: brain aging. The cognitive decline seen in the highest-intake group was equivalent to an extra 1.6 years of aging packed into just eight years. The link held true for six of the seven sweeteners studied. Only tagatose, a less common natural sweetener, 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 Suemoto.
Everyone’s Affected
Common wisdom suggests that cognitive decline is a problem for the elderly. Yet, in this study, the disturbing link between sweeteners and a rapidly aging brain was found exclusively in participants younger than 60. For those over 60, the association vanished.
This finding surprised even the researchers, who had expected the association to be more evident in older adults, since they are at higher risk of dementia and cognitive impairment.
The effect was also amplified in people with diabetes. While the link existed for everyone under 60, it was significantly stronger for participants with the metabolic disorder. This is all the more concerning as people with diabetes are precisely the demographic most encouraged to use artificial sweeteners to manage their blood sugar. They are following medical advice, trying to make a healthy choice, but this study suggests that the choice could come with a hidden cognitive cost. They are caught in a dietary catch-22.
So, what does this “cognitive decline” actually feel like?
The steepest drops were seen in verbal fluency and memory. Verbal fluency is your brain’s internal “search engine”. It’s your ability to quickly retrieve words from your mental dictionary. A decline here might mean struggling to find the right word in a conversation or having more “tip-of-the-tongue” moments. A memory decline, specifically word recall, could manifest as forgetting items on a grocery list or struggling to remember details of a recent event. These aren’t just minor annoyances; they are the bedrock of our ability to communicate, work, and engage with the world.
Correlation Not Causation
There’s a key caveat, however; one we’re very familiar with: this study shows a powerful association, not definitive proof of causation. It found a link, but it doesn’t prove that sweeteners directly cause the brain to age faster.
The study also relied on participants to report their own diets, which can be notoriously inaccurate. Can you remember everything you ate and drank over the past year? Probably not perfectly. Furthermore, the study didn’t include every artificial sweetener on the market, like sucralose (Splenda) or stevia, which have become increasingly popular.
The food and drink industry was quick to highlight these limitations. Gavin Partington, director general of the British Soft Drinks Association, told The Guardian “By the authors’ own admission, this study cannot prove cause.” The International Sweeteners Association (ISA) echoed this, stating, “The reported link between sweetener consumption and cognitive decline does not prove that one causes the other,” and emphasized the “established scientific consensus” that sweeteners are safe.
Indeed, regulatory bodies like the U.S. Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) have repeatedly deemed these sweeteners safe for consumption at acceptable daily intake levels. But these rulings are never the end of the story, especially when new studies highlight data like this.
Furthermore, this new finding doesn’t exist in a vacuum. It joins a growing chorus of research questioning the long-term health effects of these sugar impostors. Previous large-scale studies have linked them to an increased risk of type 2 diabetes (the very condition they’re meant to help manage), cardiovascular disease, and even depression. The World Health Organization itself recently advised against using non-sugar sweeteners for weight control, citing a lack of long-term benefit and potential undesirable effects from long-term use.
So, how could these supposedly inert molecules be wreaking havoc on our brains?
What Could Be the Issue?
The researchers are now investigating several potential mechanisms. One leading theory involves the gut microbiome. Our intestines are home to trillions of bacteria that play a critical role in everything from digestion to immune function and even mood. Growing evidence suggests that artificial sweeteners can alter this delicate ecosystem, killing off beneficial bacteria and promoting the growth of harmful ones. This disruption can lead to systemic inflammation, a low-grade, body-wide immune response. And chronic inflammation is a known enemy of the brain, strongly implicated in cognitive decline and neurodegenerative diseases like Alzheimer’s.
Another theory is that these sweeteners confuse the brain. When you taste something sweet, your brain anticipates a rush of calories and energy. Artificial sweeteners provide the sweet taste without the calories. Over time, this mismatch may disrupt the brain’s ability to regulate appetite and metabolism. It decouples the link between taste and nutritional consequence, potentially leading to metabolic dysregulation that indirectly harms the brain.
The question for millions of consumers is, what now? The evidence isn’t conclusive enough to warrant a ban, but it’s certainly enough to warrant caution. “More research is needed to confirm our findings,” Dr. Suemoto advises. Her team is already planning follow-up studies using neuroimaging to see if they can spot physical changes in the brains of sweetener consumers.
In the meantime, she suggests looking at other alternatives to refined sugar, like “applesauce, honey, maple syrup or coconut sugar.” Of course, these still contain sugar and calories and should be used in moderation.
The study was published in the journal Neurology.
