The consumption of low- and no-calorie sweeteners, long marketed as healthier alternatives to refined sugar, may be associated with a significantly accelerated decline in cognitive function and memory, according to a comprehensive study published in the September 3, 2025, issue of Neurology®, the medical journal of the American Academy of Neurology. The research, which tracked a large cohort of adults over nearly a decade, suggests that individuals with the highest intake of certain artificial sweeteners experience a rate of brain aging and cognitive degradation substantially higher than those who consume minimal amounts. While the study identifies a robust statistical correlation, researchers emphasized that the findings establish an association rather than a definitive causal relationship.
The study arrived at a critical juncture in global public health, as the prevalence of ultra-processed foods containing sugar substitutes continues to rise. Led by Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil, the research team analyzed the long-term neurological impacts of seven specific sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. These substances are ubiquitous in modern diets, appearing in products ranging from diet sodas and flavored waters to "low-fat" yogurts and sugar-free desserts.
Methodology and Study Parameters
The investigation involved 12,772 participants from across Brazil, with an average age of 52 at the start of the observation period. This large-scale longitudinal study followed the participants for an average of eight years, providing a substantial window through which to observe the gradual changes in cognitive performance. At the onset of the study, participants completed detailed dietary questionnaires that cataloged their consumption of food and beverages over the preceding year.
To facilitate a comparative analysis, researchers categorized the participants into three distinct groups based on their total daily intake of artificial sweeteners:
- Low Consumption Group: Averaging 20 milligrams per day (mg/day).
- Moderate Consumption Group: An intermediate range of intake.
- High Consumption Group: Averaging 191 mg/day.
To put these figures into perspective, the researchers noted that the high-consumption threshold of 191 mg/day is approximately equivalent to the amount of aspartame found in a single 12-ounce can of diet soda. Among the sweeteners studied, sorbitol was the most frequently consumed, with an average intake of 64 mg/day across the study population.
Cognitive Assessment and Tracking
The primary objective of the study was to monitor changes in "executive function"—a set of mental skills that include working memory, flexible thinking, and self-control. Participants underwent a battery of standardized cognitive tests at three specific intervals: the beginning of the study, the midpoint (four years), and the conclusion (eight years).
These assessments were designed to measure various facets of brain health, 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 test of short-term and long-term memory retention.
- Processing Speed: The time it takes for an individual to perceive and respond to information.
By comparing the results of these tests over time, researchers were able to quantify the rate of cognitive decline relative to the participants’ intake of sugar substitutes.
Key Findings: Accelerated Brain Aging
The results of the study revealed a stark contrast between high-level consumers of sweeteners and those who avoided them. After adjusting for confounding variables—including age, biological sex, hypertension (high blood pressure), and existing cardiovascular disease—the researchers found that participants in the highest consumption group experienced a decline in overall thinking and memory skills that was 62% faster than those in the lowest group.
This 62% acceleration in decline is equivalent to approximately 1.6 years of additional brain aging over the eight-year study period. Even those in the middle consumption group were not immune to these effects; they exhibited a cognitive decline 35% faster than the low-consumption group, representing roughly 1.3 years of premature brain aging.
The study also highlighted specific demographic vulnerabilities. The link between sweetener consumption and cognitive decline was notably stronger in individuals with diabetes. While these individuals often turn to artificial sweeteners to manage blood glucose levels, the data suggests that the neurological trade-off may be significant. Furthermore, when the data was segmented by age, the researchers found that the association was most pronounced in participants under the age of 60. In this younger cohort, high intake was specifically linked to faster declines in verbal fluency and general cognition. Interestingly, the study did not find a statistically significant link in participants over the age of 60, suggesting that the middle-age years may be a critical window for the impact of these substances on brain health.
Individual Sweetener Performance
While most of the sweeteners studied were associated with negative outcomes, the impact was not uniform across all substances.
- Aspartame, Saccharin, and Acesulfame-K: These widely used synthetic sweeteners were all linked to faster declines in general cognition and memory.
- Sugar Alcohols (Erythritol, Sorbitol, Xylitol): Despite often being marketed as "natural" because they are found in small amounts in fruits, high consumption of these sugar alcohols was also correlated with accelerated cognitive decline.
- Tagatose: This specific sweetener stood out as the exception. The researchers found no observable link between tagatose consumption and cognitive decline, though they noted that tagatose is currently less prevalent in the food supply than aspartame or saccharin.
Contextual Background and Global Implications
The findings from the University of São Paulo add to a growing body of evidence questioning the long-term safety of non-sugar sweeteners (NSS). In May 2023, the World Health Organization (WHO) issued a conditional guideline recommending against the use of NSS to control body weight or reduce the risk of non-communicable diseases. The WHO cited potential undesirable effects from long-term use, such as an increased risk of type 2 diabetes and cardiovascular diseases.
The neurological aspect of this research introduces a new dimension to the debate. Historically, the primary concern regarding artificial sweeteners was their potential carcinogenicity—a concern that has been largely debated and, in many cases, dismissed by regulatory bodies like the FDA. However, the shift toward studying metabolic and neurological impacts reflects a more modern understanding of how diet influences the "gut-brain axis" and systemic inflammation.
Dr. Suemoto noted that while the study does not prove causation, the strength of the association warrants caution. "Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar," Suemoto stated. "However, our findings suggest certain sweeteners may have negative effects on brain health over time."
Industry and Scientific Reactions
The study is expected to draw scrutiny from the food and beverage industry, which has long maintained that artificial sweeteners are safe and effective tools for weight management and sugar reduction. Organizations such as the Calorie Control Council and the International Sweeteners Association have historically pointed to the decades of regulatory approval as evidence of safety.
However, independent neurologists and nutritionists have begun to voice concerns about the "ultra-processed" nature of the foods that typically contain these sweeteners. Dr. Suemoto’s research suggests that the cognitive decline may be part of a broader "ultra-processed food effect," where the combination of additives, lack of fiber, and synthetic ingredients disrupts normal biological processes.
"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 added, highlighting the need for a shift toward whole-food sweeteners if sugar must be replaced.
Limitations and Future Research
Despite its large sample size and rigorous testing, the study acknowledged several limitations. First, the dietary information was self-reported by participants, which introduces the possibility of recall bias—individuals may not accurately remember every item they consumed or may underreport "unhealthy" habits. Second, the study did not include every sweetener on the market, such as newer plant-based options like stevia or monk fruit.
Furthermore, because the study was observational, it cannot rule out "reverse causality." It is possible that individuals already experiencing the earliest, imperceptible stages of cognitive decline might change their dietary habits in ways that increase their sweetener intake. However, the eight-year duration and the adjustment for cardiovascular health factors provide a robust framework for the current findings.
Analysis of Implications for Public Health
The implications of this study are profound for public health policy, particularly in countries with high rates of diabetes and obesity. If artificial sweeteners are indeed contributing to cognitive decline, the "diet" versions of popular products may be creating a secondary health crisis even as they attempt to mitigate the primary crisis of sugar overconsumption.
For consumers, the takeaway is a call for moderation and a return to less processed dietary patterns. The fact that the high-consumption group reached their threshold with just one can of diet soda per day suggests that "moderate" use in the eyes of the consumer may actually be "high" use in biological terms.
The study was a massive collaborative effort, supported by the Brazilian Ministry of Health, the Ministry of Science, Technology, and Innovation, and the National Council for Scientific and Technological Development. As the medical community continues to digest these findings, the focus will likely shift toward clinical trials that can more definitively explore the mechanisms by which these chemicals interact with neural pathways and the blood-brain barrier. For now, the Neurology® report serves as a significant warning that the quest for a "free" sweet taste may come with a hidden cost to the human mind.
