A comprehensive longitudinal study involving more than 12,000 participants has identified a significant correlation between the high consumption of certain low- and no-calorie sweeteners and an accelerated decline in cognitive functions, including memory and thinking skills. Published in the September 3, 2025, issue of Neurology®, the medical journal of the American Academy of Neurology, the research suggests that while these additives are frequently marketed as healthier alternatives to refined sugar, their long-term impact on neurological health may be more complex and potentially detrimental than previously understood. Led by Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil, the study tracked a diverse cohort of adults over an average of eight years, providing one of the most detailed glimpses to date into the relationship between non-nutritive sweeteners and the aging brain.
A Deep Dive into the Longitudinal Methodology
The study’s scale and duration provide a robust foundation for its findings. Researchers analyzed data from 12,772 adults across Brazil, with an average participant age of 52 at the start of the observation period. This middle-aged demographic is particularly relevant to researchers, as it represents a critical window where lifestyle choices and dietary habits begin to manifest as long-term health outcomes, specifically regarding neurodegeneration and the onset of dementia-related symptoms.
To establish a baseline and track progression, participants underwent a rigorous battery of cognitive assessments at three distinct intervals: the beginning of the study, the midpoint (four years), and the conclusion (eight years). These tests were designed to evaluate a broad spectrum of neurological capabilities, including:
- Verbal Fluency: The ability to retrieve information from memory and articulate it clearly.
- Working Memory: The capacity to hold and manipulate information over short periods.
- Word Recall: A measure of episodic memory and the ability to retain new information.
- Processing Speed: The efficiency with which the brain receives, understands, and responds to information.
To quantify sweetener intake, participants completed comprehensive dietary questionnaires at the study’s outset. These surveys required individuals to detail their consumption habits over the preceding 12 months, specifically identifying foods and beverages containing artificial sweeteners. The researchers then categorized participants into three groups based on their average daily intake.
Quantitative Analysis of Cognitive Erosion
The data revealed a stark contrast between those who consumed the least amount of artificial sweeteners and those with the highest intake. The "lowest consumption" group averaged approximately 20 milligrams per day (mg/day), while the "highest consumption" group averaged 191 mg/day. To put these figures into a practical context, the researchers noted that the high-consumption threshold for aspartame—one of the most common sweeteners—is roughly equivalent to the amount found in a single 12-ounce can of diet soda.
After adjusting for confounding variables—including age, biological sex, education levels, and existing health conditions such as hypertension and cardiovascular disease—the results indicated that the highest consumers of these sweeteners experienced a 62% faster decline in overall cognitive function compared to the lowest consumers. In clinical terms, this acceleration is equivalent to approximately 1.6 years of additional brain aging over the eight-year study period.
Even moderate consumption showed a notable impact. Those in the middle group, who consumed more than 20 mg/day but less than 191 mg/day, exhibited a cognitive decline that was 35% faster than the lowest group, representing about 1.3 years of premature brain aging.
The Demographic Divide: Age and Diabetes Factors
One of the study’s most surprising findings was the variation in impact across different age groups. When the data was segmented by age, researchers found that the link between high sweetener consumption and cognitive decline was most pronounced in participants under the age of 60. In this younger cohort, high intake was specifically associated with faster declines in verbal fluency and general cognition. Interestingly, the same statistical link was not observed in participants who were already over the age of 60 at the start of the study. This suggests that the mid-life period may be a particularly vulnerable stage for the brain regarding the potential neurotoxic or metabolic effects of these additives.
Furthermore, the study highlighted a heightened risk for individuals living with diabetes. While a link to cognitive decline was found in the general population, the association was significantly stronger among diabetic participants. This is particularly concerning for public health officials, as people with diabetes are among the most frequent users of artificial sweeteners, often relying on them to manage blood glucose levels while satisfying a desire for sweetness.
"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," Dr. Suemoto noted in her analysis. This suggests a potential "double burden" where the very tools used to manage one chronic condition may inadvertently contribute to the progression of another.
Profiling the Sweeteners: From Aspartame to Tagatose
The study examined seven specific low- and no-calorie sweeteners, most of which are ubiquitous in the modern global food supply. The individual analysis of these substances yielded the following insights:
- Aspartame, Saccharin, and Acesulfame-K: These "first-generation" sweeteners, commonly found in diet sodas and tabletop packets, were all linked to a faster decline in overall cognition and memory.
- Erythritol, Xylitol, and Sorbitol: Often categorized as sugar alcohols, these are frequently used in "keto-friendly" products, sugar-free gums, and low-calorie desserts. Sorbitol had the highest average consumption among the study participants at 64 mg/day. All three were associated with negative cognitive outcomes.
- Tagatose: This rare sugar, which is structurally similar to fructose but has a lower glycemic index, was the only sweetener studied that showed no association with cognitive decline. This finding may open doors for future research into tagatose as a potentially safer alternative for brain health.
The researchers emphasized that these sweeteners are rarely consumed in isolation. They are primarily found in ultra-processed foods (UPFs), including flavored waters, energy drinks, yogurts, and "light" snacks. This raises questions about whether the sweeteners themselves are the primary drivers of decline or if they serve as a marker for a diet high in ultra-processed ingredients, which have been independently linked to poor health outcomes.
The Role of Ultra-Processed Foods in Cognitive Health
The context of the Brazilian study is crucial for understanding the broader implications. Brazil has been a pioneer in nutrition science, particularly through the development of the NOVA food classification system, which categorizes foods by the extent of their processing. The sweeteners identified in the Neurology study are hallmark ingredients of Group 4: Ultra-processed foods.
The background context of the study suggests that the rise in artificial sweetener consumption is intrinsically tied to the global "nutrition transition," where traditional diets based on whole foods are replaced by industrialized products. These products are engineered to be hyper-palatable, shelf-stable, and often, low in calories. However, the study adds to a growing body of evidence suggesting that "low calorie" does not necessarily equate to "low risk."
Inferred reactions from the scientific community suggest a cautious but concerned stance. While the food industry often points to the regulatory approval of these sweeteners by bodies like the FDA and EFSA, researchers like Suemoto argue that current safety standards may not sufficiently account for long-term neurological impacts or the synergistic effects of consuming multiple types of sweeteners over decades.
Scientific Limitations and the Causality Debate
Despite the compelling nature of the data, the researchers were careful to note the study’s limitations. Most importantly, as an observational study, it demonstrates a correlation but does not prove a definitive cause-and-effect relationship. It is possible that "reverse causality" could be a factor—individuals who already sense a decline in health or cognition might switch to artificial sweeteners in an attempt to improve their diet.
Additionally, the study relied on self-reported dietary information. Participant recall is notoriously subject to error, and individuals may underreport their consumption of "unhealthy" items or fail to recognize sweeteners hidden in complex ingredient lists. Furthermore, several newer or less common sweeteners, such as stevia, monk fruit, and neotame, were not included in this specific analysis, leaving a gap in the understanding of the full spectrum of sugar alternatives.
Global Implications for Dietary Guidelines and Public Health
The implications of this study are far-reaching, particularly as global health organizations re-evaluate their stance on non-sugar sweeteners (NSS). In 2023, the World Health Organization (WHO) issued a conditional guideline suggesting that NSS should not be used as a means of achieving weight control or reducing the risk of non-communicable diseases. The findings from Brazil provide significant neurological data to support this cautious approach.
The study was a massive undertaking supported by the Brazilian Ministry of Health, the Ministry of Science, Technology, and Innovation, and the National Council for Scientific and Technological Development. This high-level governmental backing underscores the importance Brazilian authorities place on addressing the long-term effects of industrial food additives on an aging population.
Looking forward, Dr. Suemoto and her team are calling for more intensive research into "natural" refined sugar alternatives. "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," she stated. While these alternatives contain calories and affect blood sugar, they may lack the specific neuro-disruptive properties associated with synthetic or highly refined chemical sweeteners.
As the global population ages and the prevalence of cognitive impairment rises, the findings of this study serve as a critical warning. They suggest that the quest for a "free lunch" in nutrition—sweetness without the metabolic cost of sugar—may come with a hidden price tag paid by the brain. For consumers, the takeaway is clear: moderation and a return to less processed dietary patterns may be the most effective strategy for preserving cognitive longevity.