For many years people have changed from drinking regular soda to drinking diet soda, thinking that they were making the right choice in terms of health.
No sugar. No calories. So what’s the issue?
A 2026 study is now casting some serious doubt on that assumption—particularly with regard to long-term brain health and dementia.
The New Study: Diet Soda & Dementia
The researchers looked at the data collected as part of the long-running Northern Manhattan Study, focusing on the 947 adults who were free from dementia when the cognitive testing began.
The findings deserve attention:
In the researchers’ main analysis, the risk of dementia increased by 39 per cent for each extra diet soda consumed per day.
Even more striking:
Those who drank more than one diet soda each day had about four times the risk of developing dementia than those who drank one or fewer per day.
Dementia was eventually diagnosed in around 20 per cent of the participants.
Interestingly, the researchers found no statistically significant association between the regular consumption of sugar-sweetened soda and dementia in this study.
This Isn’t the First Warning Sign
The study is not something that exists by itself.
An earlier analysis of the Framingham Heart Study showed that people who drank artificially sweetened beverages every day had nearly three times the risk of developing Alzheimer’s disease as compared with those who did not consume such beverages.
A systematic review and meta-analysis carried out in 2025 found that a higher consumption of artificially sweetened drinks was linked to a 42% increased risk of Alzheimer’s disease.
There is also some research which focuses on artificial sweeteners and cognitive performance; an eight-year prospective study found that a higher intake of several low- and no-calorie sweeteners—such as aspartame, saccharin and acesulfame-K—was linked to more rapid declines in general cognitive function, especially in respect to memory and verbal fluency.
But Does Diet Soda Cause Dementia?
It doesn’t have to be, and this point is of great importance.
They are mainly based on observational studies; while they can show an association, they cannot demonstrate that diet soda or artificial sweeteners caused dementia directly.
The Northern Manhattan study now offers a particularly important clue.
The link between diet soda and dementia disappeared when the researchers excluded those who were obese or had diabetes.
This might indicate that underlying metabolic dysfunction is making a significant contribution to the relationship, and it also brings up the possibility of reverse causation—that is, people who are already dealing with obesity, diabetes, or other metabolic issues may be more likely to switch from regular soda to diet soda.
That’s why we shouldn’t interpret this research as:
If you drink a Diet Coke, you will get dementia.
We should not overlook the increasing amount of research that indicates that the kinds of drinks we consume and our metabolic health could affect the way our brains age.
What is the bigger issue? What is your brain being exposed to every day?
Brain health is not the result of a single ingredient.
Think about the cumulative signals your body receives every day:
Blood sugar and insulin resistance.
Ultra-processed foods.
Artificial sweeteners.
Poor sleep.
Chronic stress.
Inflammation.
Physical inactivity.
Environmental exposures.
One exposure may seem minor.
If this kind of signal is carried on from day to day and year after year, then it can accumulate.
Which is why I always return to the basic principles of health rather than merely addressing the symptoms once they show up.
Three Things You Can Do Today
1. Check what you’re drinking.
Water should form the bulk of your hydration, and as alternatives, unsweetened sparkling water, mineral water, coffee and tea can be considered depending on the individual.
2. It doesn’t follow that “sugar-free” means it’s healthy.
Check the ingredient labels and note how often artificial sweeteners appear during the day, not just in soda.
3. Looking after your metabolic health will help with the health of your brain.
Some of the most important long-term investments you can make in your cognitive health are exercise, maintaining muscle mass, getting quality sleep, regulating your blood sugar and tackling metabolic dysfunction.The Take-Home Message
We cannot yet say that diet soda causes dementia.
Yet when a new study shows that people who consume more than one diet soda a day have about four times the risk of dementia, it is worth our attention—especially since earlier research has expressed similar concerns.
The goal isn’t fear.
It’s awareness.
The things you expose your body to today could affect how your brain works decades from now.
Sometimes one of the simplest places to start improving your health is also one of the easiest:
Check the contents of your glass.
