Aspartame in diet drinks linked to potential heart and brain changes in mice, study finds

A Spanish study on mice found that higher intake of aspartame—the artificial sweetener used in Diet Coke, Sprite and Extra chewing gum—was associated with a roughly 20% increase in mild cardiac hypertrophy and signs of accelerated cognitive decline. In the experiment, mice received an aspartame dose of 7 milligrams per kilogram of body weight over three consecutive days every two weeks, a regimen researchers described as roughly equivalent to about three servings every fortnight for humans. The study's authors noted that global health authorities — including the World Health Organization, the European Medicines Agency and the U.S. Food and Drug Administration — advise a daily limit of about 50 milligrams per kilogram of body weight, a level many consider higher than typical consumer exposure.

Over a year of follow-up, the mice exposed to aspartame showed a notable reduction in heart function, with left-ventricle output falling by 26% and right-ventricle output by 20%. The septal curvature—the thickness of the muscular wall separating the heart’s two ventricles—was reduced by 25%. In parallel, the animals exhibited signs of altered neurobehavior and possible pathophysiological changes in the brain. The researchers reported that body fat dropped by about 20% in the treated mice, a finding they described as a potential trade-off of the reported cardiac and cognitive effects.

The research team, based at the Centre for Cooperative Research in Biomaterials in San Sebastián, cautioned that the findings should not be extrapolated to humans without further study. They emphasized several limitations, including the study length and the intrinsic differences between mice and human physiology. Still, they urged officials to reassess current aspartame consumption guidelines in light of the observed cardiovascular and cognitive changes.

The International Sweeteners Association (ISA) urged caution in interpreting the results, noting that differences between humans and mice in metabolism, lifespan and cardiac and brain energy use limit the direct applicability of the findings. “Key physiological differences between humans and mice…limit the relevance of the study’s conclusions,” said Laurent Oger, the ISA’s director general. He added that reductions in body weight and fat observed in mice do not necessarily mirror outcomes in human clinical trials, where low- or no-calorie sweeteners have not consistently shown independent effects on body weight, though they may help reduce overall sugar intake.

Researchers also highlighted the broader context of artificial sweeteners. Previous work has tied aspartame to concerns ranging from cancer risk to cardiovascular events, and in 2023 the World Health Organization classified aspartame as possibly carcinogenic to humans. The UN agency stressed that risk applies to very high levels of consumption, stating that a 70-kilogram (11-stone) adult could safely drink around 14 cans of diet fizzy drinks per day under its risk estimates. Experts emphasize that these classifications relate to high-end intake and do not automatically translate into everyday consumer behavior.

The study, published in Biomedicine and Pharmacotherapy, underscores the need for more comprehensive research to determine whether the observed heart and brain effects in mice might ever translate to humans and, if so, under what consumption patterns. In the meantime, health authorities continue to evaluate acceptable daily intakes and to provide guidance balanced against the benefits of weight management and sugar reduction versus potential risks. Researchers and public health officials alike say clear, long-term human data are essential before revising official safety limits for aspartame.

In the wake of ongoing debates about artificial sweeteners, clinicians and policymakers stress moderation and a preference for a varied diet. For some individuals, limiting or avoiding aspartame and other non-nutritive sweeteners may be prudent, particularly for those with preexisting heart or cognitive concerns. As researchers pursue longer-term studies, the broader question remains how best to weigh sugar reduction goals against potential unintended effects from substitutes used to achieve them.