Sweeteners and Thinking Skills: What the 8-Year Brazilian Study Found

What people see in the news

Headlines say diet soda may be ageing your brain. The story behind them is a real study, published in the journal Neurology on September 3, 2025. It followed 12,772 adults in Brazil for about eight years.

We cover it here for one reason. People who read about sweeteners usually want to know about cancer, and this study did not measure cancer at all. It measured thinking and memory. Those are different questions with different evidence behind them.

What the study actually found

Researchers led by Claudia Kimie Suemoto at the University of São Paulo tracked seven low- and no-calorie sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose.

Participants were around 52 years old on average. The team sorted them into three groups by how much sweetener they ate, then tested memory, language and thinking skills over time.

• The highest-intake group's scores declined about 63% faster than the lowest group. Researchers described that as roughly 1.6 years of extra brain ageing.
• The middle group declined about 36% faster, or roughly 1.3 years.
• Six of the seven sweeteners were individually linked to faster decline. Tagatose was not.
• Memory was the area most affected.
• The link was stronger in people under 60 and in people with diabetes. In people over 60, researchers found no link.

The amounts matter, and they are smaller than the headlines suggest. The lowest group averaged 20 mg a day. The highest averaged 191 mg a day. For comparison, the FDA's acceptable daily intake for aspartame is 50 mg per kilogram of body weight — for a 60 kg adult, that is 3,000 mg a day, which the FDA illustrates as about 75 tabletop sweetener packets.

So the highest-consuming group in this study was well inside the FDA's safety limit. That cuts both ways. It means the finding is not about extreme intake. It also means the study cannot tell us the limit is wrong.

What this does not mean

This is not a cancer study. It measured cognition. It says nothing about whether sweeteners cause cancer, and it did not look.

It cannot show cause. This was an observational study. It can find a pattern; it cannot prove sweeteners caused the decline. People who consume a lot of sweeteners may differ in other ways — weight, diabetes, overall diet, activity, education — and while researchers adjust for such things, adjustment is never complete.

Diet was self-reported. Participants described what they ate, and people misremember. The study authors list this as a limitation.

It did not cover every sweetener. Sucralose and stevia, both widely used, were not among the seven.

The study author's own view was measured. She cautioned against drawing firm conclusions from a single study, and suggested occasional diet soda is unlikely to be the concern.

Where the cancer question actually stands

That is a separate body of evidence, and we cover it in detail:

• Aspartame and Cancer: What IARC's Review Means — why the 2023 "possibly carcinogenic" classification is weaker than it sounds
• Do Artificial Sweeteners Cause Cancer? — the broader picture
• Saccharin and Cancer: Why It Was Cleared — a sweetener once thought to cause cancer in humans, and why that changed
• IARC Group 2B: "Possibly Carcinogenic" — what that label does and does not claim

The short version: IARC placed aspartame in Group 2B in 2023, a category that means the evidence is limited, not that the risk is established. It is the same group that contains aloe vera extract and pickled vegetables. Meanwhile the international committee that sets intake limits reviewed the same evidence and left the acceptable daily intake unchanged.

Questions to ask a healthcare team

• I have diabetes and use sweeteners — does this change anything for me?
• Is there a reason in my situation to prefer water, or to cut back?
• Does anything I am taking or being treated for interact with what I drink?
• I am worried about my memory. Is what I am noticing worth testing?

If you want a practical takeaway

There isn't a cancer reason in this study to change what you drink. If you would like to cut back anyway, that is a reasonable thing to want, and it is a conversation to have with your own clinician rather than with a headline.

Free, plain-language explanation of what studies like this do and do not show is part of why Cancer Explained exists.

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Prepared by Cancer Explained's AI-assisted editorial system and checked against the sources listed below. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown.

Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.

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