The short answer is yes, you should pay attention, but no, you do not need to panic. A large 2025 study published in the journal Neurology found that people who consumed the most artificial sweeteners experienced 62 percent faster cognitive decline over eight years compared to the lowest consumers, an effect the researchers described as equivalent to 1.6 additional years of brain aging. That is a meaningful finding, especially if you are someone who drinks a daily diet soda containing 200 to 300 milligrams of artificial sweetener and already has risk factors for dementia. But the research comes with serious caveats that change how you should interpret the headlines. Every study linking artificial sweeteners to cognitive decline is observational, meaning scientists watched what happened over time rather than randomly assigning people to drink diet soda or skip it.
That distinction matters enormously because it means we cannot say artificial sweeteners cause dementia. People who consume large amounts of these sweeteners often do so because they already have diabetes or obesity, conditions that independently raise dementia risk. So the connection may be real, or it may be a statistical shadow cast by other health problems. This article walks through the major studies, including the 2025 Brazilian cohort research, the Framingham Heart Study findings, and a 2026 Northern Manhattan Study that complicates the picture further. We will look at which specific sweeteners have been flagged, what the FDA actually says, who faces the highest risk, and what practical steps make sense given the current evidence.
Table of Contents
- What Does the Research Actually Say About Artificial Sweeteners and Dementia Risk?
- Why the Diet Soda-Dementia Link May Not Be What It Seems
- Which Artificial Sweeteners Have Been Flagged and Which Have Not
- What the FDA Says and Why That Matters for Your Decisions
- Age, Diabetes, and Who Faces the Greatest Risk
- Practical Alternatives When You Want to Cut Back
- What We Still Do Not Know and What Comes Next
- Conclusion
- Frequently Asked Questions
What Does the Research Actually Say About Artificial Sweeteners and Dementia Risk?
The most cited recent evidence comes from a study of 12,772 adults in Brazil, published in Neurology in September 2025. Researchers followed participants with an average age of 51.9 for eight years and measured their intake of artificial sweeteners alongside cognitive performance over time. Those in the highest consumption group, averaging about 191 milligrams per day, showed significantly faster declines in global cognition compared to the lowest consumers. The decline was most pronounced in memory and verbal fluency, the very domains that erode earliest in Alzheimer’s disease. Six specific sweeteners were implicated: aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol. Notably, tagatose, a less common sugar substitute, showed no link to cognitive decline at all. This was not the first warning.
Back in 2017, the Framingham Heart Study reported that people who drank at least one diet soda per day were roughly three times more likely to have a stroke or develop Alzheimer’s disease over a ten-year period. That finding made headlines, though the absolute numbers were modest: about 3 percent of participants had strokes and roughly 5 percent developed dementia. Then in early 2026, data from the Northern Manhattan Study found that adults drinking more than one diet soda daily had approximately four times the dementia risk. That is a striking number, but it came with a critical footnote we will address shortly. What makes these findings difficult to dismiss outright is the consistency across different populations and study designs. Brazilian adults, American participants in Framingham, older adults in Manhattan: the pattern keeps appearing. But consistency of association is not proof of causation, and every one of these research teams has acknowledged that their results cannot establish a direct cause-and-effect relationship.
Why the Diet Soda-Dementia Link May Not Be What It Seems
The Northern Manhattan Study offers the clearest illustration of why you should interpret these headlines carefully. Among 947 dementia-free adults with a mean age of 64, frequent diet soda consumption was associated with a roughly fourfold increase in dementia risk. That sounds alarming in isolation. However, when the researchers excluded participants who had obesity or diabetes, the association disappeared entirely. This finding raises an uncomfortable possibility: diet soda consumption may simply be a marker for people who already have metabolic conditions that drive dementia, not an independent cause of cognitive decline. This problem, known as reverse causality, haunts virtually all research on artificial sweeteners and brain health. People do not randomly choose to drink diet soda.
They switch to it because a doctor told them to lose weight, because they received a diabetes diagnosis, or because they are trying to manage blood sugar. These underlying conditions, not the sweetener itself, may be doing the real damage. The 2025 Brazilian study attempted to control for confounders like body mass index, diabetes status, and overall diet quality, and the association persisted. But observational studies can never fully eliminate confounding, and no randomized controlled trial has ever tested whether artificial sweeteners directly harm cognition. If you are someone without diabetes, without obesity, and without other metabolic risk factors, the current evidence is far less concerning for you personally. That is not permission to ignore it, but it is a reason to resist the impulse to treat a diet soda as equivalent to a toxin. Context matters, and your individual health profile changes how these population-level findings apply to you.
Which Artificial Sweeteners Have Been Flagged and Which Have Not
Not all sugar substitutes carry the same signals in the research. The 2025 Neurology study specifically identified six sweeteners associated with faster cognitive decline: aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol. These are found in an enormous range of products, from diet sodas and sugar-free gum to protein bars and flavored water. Aspartame alone appears in thousands of food and beverage products worldwide and remains one of the most studied food additives in history. Acesulfame-K is frequently paired with other sweeteners in zero-calorie drinks to improve taste. Interestingly, tagatose stood apart.
This naturally occurring sugar, found in small amounts in dairy products, showed no association with cognitive decline in the Brazilian study. Tagatose is less commonly used than the other six sweeteners and has a different metabolic profile, being partially absorbed in the small intestine rather than passing through the body undigested like many artificial sweeteners. While it would be premature to recommend tagatose as a definitively safe alternative based on a single study, its absence from the list of concerning sweeteners is worth noting for people who are actively trying to reduce their intake of the flagged compounds. For practical purposes, the highest daily exposures come from beverages. A single can of diet soda typically contains 200 to 300 milligrams of artificial sweetener, which already approaches or exceeds the 191-milligram daily average seen in the high-consumption group of the Brazilian study. Tabletop sweetener packets, sugar-free desserts, and flavored yogurts add to the total, often without people realizing how much they are consuming across an entire day.
What the FDA Says and Why That Matters for Your Decisions
The U.S. Food and Drug Administration has approved six high-intensity sweeteners and maintains that they are “safe for the general population under certain conditions of use.” Despite the accumulating observational evidence linking sweetener consumption to cognitive decline, the FDA has not changed its safety assessments. This is not necessarily negligence. The agency’s standard for revising an approval typically requires stronger evidence than observational associations, particularly when confounding factors remain unresolved. The FDA’s position was tested in 2023 when the World Health Organization’s International Agency for Research on Cancer classified aspartame as “possibly carcinogenic.” The FDA publicly disagreed with that classification, arguing that the evidence did not support it. That disagreement tells you something important about how regulatory agencies weigh population-level signals against the standard of proof they require.
For dementia specifically, the bar is even higher because no interventional study has demonstrated harm. Regulators tend to wait for mechanistic evidence or controlled trials before acting, and neither exists yet for the sweetener-cognition question. What this means practically is that you cannot rely on FDA approval as a guarantee that heavy sweetener consumption is harmless to your brain. Regulatory absence of concern is not the same as evidence of safety, particularly for outcomes like dementia that take decades to develop. At the same time, the FDA’s position reflects a genuine scientific reality: we do not yet have proof that these substances cause cognitive harm. You are making decisions under uncertainty, and the honest answer is that both continuing and discontinuing artificial sweeteners involve tradeoffs.
Age, Diabetes, and Who Faces the Greatest Risk
One of the more surprising findings from the 2025 Brazilian study is that the association between artificial sweeteners and cognitive decline was stronger in people under 60 than in those over 60. The researchers found no significant link in the older group at all. This is counterintuitive since older adults are the ones most commonly developing dementia, but it may reflect the fact that cognitive decline in people over 60 is driven by so many competing factors that the sweetener signal gets lost in the noise. Alternatively, it may suggest that earlier, long-term exposure during midlife is where the potential damage accumulates. The finding that the association was stronger in people with diabetes adds another layer of concern.
Diabetes is already one of the most well-established modifiable risk factors for dementia, and people with diabetes are among the heaviest consumers of artificial sweeteners. If sweeteners compound the cognitive risk that diabetes already creates, this subgroup faces a particularly difficult situation: the very products they use to manage blood sugar may be contributing to another serious health threat. But the Northern Manhattan Study’s finding that the association vanishes when metabolic conditions are excluded suggests caution before drawing that conclusion too firmly. If you are in midlife, have diabetes or prediabetes, and drink multiple diet sodas daily, the current evidence points most directly at you as someone who should consider reducing intake. This is not because the science has proven causation but because you sit at the intersection of multiple risk factors, and the precautionary principle has more weight when the potential downside is irreversible cognitive decline.
Practical Alternatives When You Want to Cut Back
Reducing artificial sweetener intake does not mean returning to sugar-sweetened beverages, which carry their own well-documented risks for metabolic health and, indirectly, for dementia. Sparkling water with a slice of lemon or lime provides the carbonation many diet soda drinkers actually crave. Unsweetened iced tea, brewed strong and chilled, offers flavor complexity without any sweetener at all.
For people who find the transition difficult, gradually diluting diet soda with plain sparkling water over several weeks can ease the adjustment period. Some people wonder about stevia and monk fruit extract, two plant-derived sweeteners that were not among the six flagged in the 2025 study. The absence of evidence against them is not the same as evidence of safety, but it does mean they have not shown the same associational signals in the research conducted so far. If you are looking for a sweetened option and want to avoid the specific compounds that have raised concerns, these may be reasonable choices while the science continues to develop.
What We Still Do Not Know and What Comes Next
The single biggest gap in this research is the absence of any randomized controlled trial. Every finding discussed in this article comes from watching groups of people over time and measuring what happened. That approach can reveal patterns, but it cannot prove that one thing caused another. Designing a trial where you randomly assign thousands of people to consume artificial sweeteners or avoid them for a decade or more is logistically daunting and ethically complicated, which is why it has not been done. Until it is, we are making judgments based on incomplete evidence.
Mechanistic research may offer answers sooner. Some laboratory studies have suggested that certain artificial sweeteners alter gut bacteria in ways that increase inflammation, a known contributor to neurodegeneration. Others have explored whether sweeteners cross the blood-brain barrier and directly affect neural tissue. These lines of investigation are in early stages but could eventually provide the biological plausibility that would strengthen or weaken the case against specific sweeteners. For now, the most honest summary is that the evidence is concerning enough to warrant attention but not conclusive enough to warrant alarm.
Conclusion
The research linking artificial sweeteners to cognitive decline is real, growing, and not easily dismissed. Multiple studies across different populations have found that heavy consumers of diet beverages and artificial sweeteners show faster cognitive decline and higher dementia risk. The 2025 Neurology study, the largest and most recent, identified six specific sweeteners associated with the equivalent of 1.6 years of additional brain aging. These findings deserve to be taken seriously, particularly by people in midlife and those with diabetes or metabolic conditions.
But the evidence is not yet definitive. Every study is observational, reverse causality remains a plausible alternative explanation, and the FDA has not altered its safety stance. The most reasonable approach is moderation: if you currently drink multiple diet sodas daily, consider cutting back and replacing some of that intake with unsweetened alternatives. If you have an occasional diet drink, the current evidence does not suggest you face meaningful risk. Stay attentive as new research emerges, discuss your specific situation with your doctor, and remember that the strongest evidence-based strategies for protecting your brain remain physical exercise, social engagement, blood pressure management, and treating diabetes effectively.
Frequently Asked Questions
Does drinking one diet soda a day cause dementia?
No single study has proven that one diet soda per day causes dementia. The Framingham Heart Study found that one or more diet sodas daily was associated with roughly three times the risk of stroke or Alzheimer’s over ten years, but the absolute rates were low and the study was observational. Association is not the same as causation.
Which artificial sweeteners are linked to cognitive decline?
The 2025 Neurology study identified six: aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol. Tagatose, a less common sweetener, showed no association with cognitive decline in the same study.
Is stevia safer for brain health than aspartame?
Stevia was not among the sweeteners flagged in the major 2025 study, but that does not mean it has been proven safe for long-term brain health. It simply has not shown the same associational signals in the current research. More study is needed.
Should people with diabetes stop using artificial sweeteners?
This is a decision to make with your doctor. The 2025 study found a stronger association between sweeteners and cognitive decline in people with diabetes. However, switching back to sugar carries its own serious risks for blood sugar management. Reducing overall sweetener intake while exploring unsweetened alternatives may be a balanced approach.
At what age does artificial sweetener consumption matter most for brain health?
The 2025 Brazilian study found that the association between sweetener intake and cognitive decline was stronger in people under 60 and was not detected in those over 60. This suggests that midlife consumption patterns may be particularly relevant.
Has the FDA warned against artificial sweeteners for brain health?
No. The FDA maintains that approved artificial sweeteners are safe for the general population under certain conditions of use. The agency has not revised its position based on the recent cognitive decline studies and publicly disagreed with the WHO’s 2023 classification of aspartame as possibly carcinogenic.
