By Sandee LaMotte, CNN

(CNN) — People who consumed the highest levels of certain artificial sweeteners — equivalent to just one diet soda a day — saw a significant decline in their ability to remember and recall words when compared to people who consumed the lowest levels, a new study found.

“People who consumed the most low- or no-calorie sweeteners showed a 62% faster global cognitive decline than those who consumed the lowest amount — that’s the equivalent of 1.6 — years of brain aging,” said lead study author Dr. Claudia Kimie Suemoto, an associate professor of geriatrics and director of the Biobank for Aging Studies at the University of São Paulo’s Medical School in Brazil.

People in the highest tier consumed an average of 191 milligrams, or about 1 teaspoon, of artificial sweeteners each day. To put that into perspective, one can of diet soda sweetened with aspartame contains around 200 to 300 milligrams, according to the World Health Organization.

A middle tier of people consumed an average of 66 milligrams of artificial sweeteners a day, with the lowest consumption at only 20 milligrams a day, according to Suemoto.

“Participants in the middle tier had a 35% faster rate of global cognitive decline — which is about 1.3 years of aging — than people who consumed the lowest amount of these sweeteners,” she said. “Now, the study is only observational — I cannot say to you that artificial sweeteners cause cognitive decline. We do know, however, that these sweeteners are associated with worse cognitive trajectories.”

Non-nutritive sweeteners are often used in low-sugar ultraprocessed foods and specialty products created for people with diabetes, according to the study published Wednesday in Neurology, the medical journal of the American Academy of Neurology.

“The widespread assumption that LNCS (low- and no-calorie sweeteners) represent a safe sugar substitute may be misguided, especially given their ubiquity in products marketed as ‘healthier’ alternatives,” said Dr. Thomas Holland, writing in an editorial published in concert with the study.

“The biological mechanisms underlying these findings hold particular relevance for neurologists and health care professionals who manage patients with cerebrovascular disease and cognitive impairment,” said Holland, an instructor in the department of internal medicine, a division of digestive diseases and nutrition at Rush University’s Institute for Healthy Aging in Chicago.

The International Sweeteners Association (ISA), which represents the industry, told CNN in an email that sweeteners provide a safe and effective way to reduce sugar and calorie intake, a key public health goal for managing conditions such as obesity and type 2 diabetes.

“While the study has garnered media attention, it is essential to place its results within the broader, established scientific consensus on sweeteners safety,” the ISA said. “The safety of low/no calorie sweeteners has been consistently confirmed by leading global health authorities.”

Cognitive aging worse for people with diabetes

Researchers analyzed the diet and cognitive abilities of nearly 13,000 Brazilians between the ages of 35 and 75 participating in the Brazilian Longitudinal Study of Adult Health.

Dietary information was collected at the start of the study, or baseline, and a battery of cognitive tests were administered three times over an average of eight years. The tests accessed verbal fluency, working memory, word recall and processing speed.

Working memory is the ability to hold information needed to accomplish complex mental tasks such as learning, reasoning and problem-solving. It’s often measured by asking people to remember certain words or numbers in a series. Verbal fluency is the ability to rapidly and spontaneously produce appropriate words when speaking. It’s often measured by asking people to name as many words as they can which start with a specific letter.

If a person had diabetes, the decline in memory and global cognition was even more pronounced, Suemoto said, likely because their overall exposure may be higher than people without the condition.

“In addition, diabetes itself is already a strong risk factor for cognitive decline related to Alzheimer’s disease and vascular dementia, which probably makes the brain more vulnerable to harmful exposures,” she added. “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.”

When researchers analyzed the results by age, they found people under the age of 60 who consumed the highest amounts of sweeteners showed faster declines in verbal fluency and overall cognition. That finding did not apply to those over age 60, however.

“This suggests that midlife dietary exposures, decades before cognitive symptoms emerge, may carry life-long consequences for brain health,” Holland said in the editorial.

“These findings may prompt neurologists to reconsider standard dietary recommendations, particularly for patients with diabetes, metabolic syndrome, or cerebrovascular risk factors.”

Not all sweeteners were linked to decline

Researchers looked at the following artificial sweeteners for the study: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose.

Tagatose was not connected to cognitive decline in the study. Tagatose is a monosaccharide, or simple sugar, just like fructose and glucose. Because it’s found naturally in so few plants, it’s considered a rare sugar, but it can be manufactured using chemicals or a complex and costly enzymatic process.

However, consumption of the other non-nutritive sweeteners was associated with a faster decline in global cognition, particularly in working memory and verbal fluency, according to the study.

Saccharin, acesulfame-K and aspartame are well-established artificial sweeteners that are considered GRAS or “generally recognized as safe” by the US Food and Drug Administration. The FDA has set limits for these and many other similar low- and no-calorie sweeteners on its website.

The World Health Organization, however, announced in July, 2023 that aspartame was “possibly carcinogenic to humans,” a decision the FDA dismissed.

Erythritol, xylitol and sorbitol are sugar alcohols, a carbohydrate found naturally in tiny quantities in foods such as cauliflower, eggplant, lettuce, mushrooms, spinach, plums, raspberries and strawberries.

Manufacturers artificially create sugar alcohols and use them as bulking sugars to cut the intense sweetness of other no-calorie sweeteners such as aspartame. Sugar alcohols such as erythritol can be found in diet sodas and teas, chewing gum, candies, chocolate, bakery products, keto-friendly ice cream and more.

Studies have shown that both erythritol and xylitol may cause blood platelets to more easily clump — creating clots that can break off and travel to the heart, triggering a heart attack, or to the brain, damaging blood vessels or triggering a stroke.

Dr. Stanley Hazen, lead author of the erythritol and xylitol studies, called the Brazilian study “intriguing and concerning.” Hazan is the director of the Center for Cardiovascular Diagnostics and Prevention at the Cleveland Clinic Lerner Research Institute.

While the study has limitations, including the use of only one diet survey that relied on subject recall, “the large and diverse cohort mix and consistency of findings in both diabetics and non-diabetics alike support the reproducibility of the findings,” said Hazen, who was not involved with the new study.

“Studies such as this and ours add to the growing body of data questioning both the long-term safety of artificial or non-nutritive sweeteners – and the designation of GRAS for these agents.”

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