Diet soda and your brain: do artificial sweeteners really age it by 1.6 years?

If you work at a screen, there is a fair chance a can of something sugar-free is within reach. It felt like the responsible choice: the caffeine without the sugar. Then, in September 2025, a study in Neurology produced a headline that travelled fast. People who consumed the most artificial sweeteners, it reported, showed cognitive decline equivalent to 1.6 extra years of ageing.

That number is real, in the sense that it came out of a real analysis of real people. Whether it means your drink is ageing your brain is a separate question, and the answer requires looking at what kind of study this was, who was in it, and what it could not rule out.

What the study actually did

The data came from ELSA-Brasil, a long-running study of Brazilian civil servants. The final sample included 12,772 adults, with an average age of 52 at baseline. At the start, each person filled in a questionnaire about what they had eaten over the past year. Their memory, verbal fluency and general thinking skills were then tested three times over roughly eight years.

The researchers estimated each person’s intake of seven sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. They then split people into three groups by total intake and compared how fast each group’s test scores fell.

Those consuming the highest amounts, about 191 milligrams per day on average, experienced a 62 percent faster cognitive decline compared to the lowest group, with results equivalent to 1.6 years of ageing. The middle group also declined more rapidly, by 35 percent. The decline was clearest in memory and verbal fluency.

So far, so alarming. Now the details that complicate it.

Three odd things in the results

It only showed up in younger people. The researchers found a link in people under 60 but not older than 60. That is strange. Cognitive decline is far more common after 60, so if sweeteners damaged the brain you would expect the signal to be loudest there. The authors’ explanation is that midlife is when exposures matter most. An equally plausible one is that something else differs about middle-aged heavy users of diet products.

It may have been stronger in people with diabetes, a subgroup result that cuts two ways. It could mean people with diabetes are more vulnerable. It could also mean the sweetener is partly a marker for the diabetes, since people with diabetes are the group most likely to be told to use sweeteners in the first place.

One sweetener was innocent. Tagatose showed no association. It is a rarely used sweetener, so the result may simply be a lack of data, but it is a reminder that the seven were lumped together for the headline figure despite being chemically unrelated. Three of them (erythritol, xylitol and sorbitol) are sugar alcohols, a different class from aspartame and saccharin. And two of the most widely used sweeteners in current diet drinks, sucralose and stevia, were not among the seven studied at all.

The problem no adjustment can fully fix

Ask why a 50-year-old drinks diet cola instead of regular, and the most common answers are weight, blood sugar, or a doctor’s advice. People move to sweeteners because they already have a health concern, and those same concerns (obesity, high blood sugar, high blood pressure) are risk factors for cognitive decline.

This is reverse causation, and it haunts all sweetener research. Studies like this adjust for such factors where they can, which is good practice. But adjustment only works for what was measured, measured well, and measured at the right time. Someone whose blood sugar was creeping up for a decade before the study began looks the same in the dataset as someone whose was not.

The diet data add a second weakness. Intake was estimated from a single food questionnaire at the start, relying on memory of the previous year, and then assumed to describe the following eight. Reporting of the limitations notes the reliance on self-reported diet data and the exclusion of some lesser-used sweeteners.

The researchers were careful to note that the study shows links, not proof that sweeteners cause cognitive decline.

Where this sits in the wider picture

This is not the first warning about sweeteners, and it would be wrong to dismiss it as a one-off.

In 2023 the World Health Organization issued a guideline that recommends against the use of non-sugar sweeteners to control body weight. Its systematic review found that they do not confer any long-term benefit in reducing body fat in adults or children, and that there may be potential undesirable effects from long-term use, such as an increased risk of type 2 diabetes, cardiovascular diseases, and mortality in adults.

Two things about that guideline are worth knowing. The recommendation was graded conditional, which is the WHO’s way of saying the evidence is uncertain, largely because of the same reverse causation problem. And it explicitly does not cover sugar alcohols, three of which were in the Brazilian study.

The industry disputes all of it. The Calorie Control Council, which represents manufacturers, responded that a substantial body of evidence shows these sweeteners provide effective and safe options to reduce sugar and calorie consumption. That is an interested party, and its position should be weighed accordingly.

What is not known

Whether sweeteners cause cognitive decline. No trial has randomised people to sweeteners or not and followed their cognition for years, and none is likely.

Which sweeteners, if any, matter. Grouping seven different chemicals gives a tidy headline and no mechanism.

Whether the dose in one or two cans a day is relevant. The highest group averaged 191 mg a day, but intake was estimated, not measured.

Whether it replicates. This is one cohort in one country. A finding that appears only in under-60s needs to show up again somewhere else before it carries much weight.

What to do with a fridge full of diet cola

Do not switch back to sugar. The study did not compare sweeteners with sugar, and nothing in it suggests regular cola is the safer option.

Do not treat sweeteners as free, either. The WHO’s broader point is sensible regardless of the brain data: the aim is a less sweet diet overall, not the same sweetness from a different molecule.

If you drink several diet drinks a day, the low-regret move is to replace some of them with water, sparkling water, tea or coffee. That costs nothing and is reasonable under every interpretation of the evidence. One can a day is not something this study gives you grounds to lose sleep over.

This is not individual medical advice. If you have diabetes, sweeteners may be part of how you manage blood sugar, and any change belongs in a conversation with your clinician.

Common questions

Do artificial sweeteners cause memory loss?

That has not been shown. One observational study of 12,772 adults found the highest consumers had 62 percent faster cognitive decline over about eight years, but the study relied on self-reported diet and cannot separate the effect of sweeteners from the health problems that lead people to use them.

Which artificial sweeteners were linked to cognitive decline?

The study examined aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose. All except tagatose were associated with faster decline. Sucralose and stevia were not among the seven studied.

Is diet soda worse than regular soda for your brain?

Nothing in this research shows that. The study did not compare sweeteners with sugar, so it offers no reason to switch back to sugary drinks.

Why was the effect only seen in people under 60?

Nobody knows. The researchers found a link in people under 60 but not in those older, which is unexpected, since cognitive decline is more common with age. It may reflect a genuine midlife vulnerability or unmeasured differences between groups.

The bottom line

A large, serious study found that heavy users of artificial sweeteners declined faster on cognitive tests, and it cannot tell whether the sweeteners or the reasons people use them are responsible. The sensible response is proportionate: drink fewer sweet drinks of any kind, do not go back to sugar, and wait for someone to repeat the finding before treating a daily can as a threat to your memory.