The researchers caution that the study only shows an association - it does not prove that diet drinks actually cause stroke or dementia.
This does not necessarily imply causality, however, as multiple other confounders may be present. Researchers have found that while drinking sugary beverages frequently may lead to poorer memory, daily intake of diet soda may increase the risk of stroke and dementia.
"Drinking at least one artificially sweetened beverage daily was associated with nearly three times the risk of developing stroke or dementia compared to those who drank artificially sweetened beverages less than once a week", the research read, which was published in Stroke, the journal of the American Heart Association.
People might think that drinking diet soda is the healthier alternative to the more sugary options.
"Both sugar and artificially sweetened soft drinks may be hard on the brain", said senior editorial author Ralph Sacco M.D., a former president of the American Heart Association and the chairman of the Department of Neurology at the Miller School of Medicine at University of Miami in Florida.
"Association is not the same as causation, although the survival curves are impressive", Nestle said.
Science has pretty much debunked the claims that artificial sweeteners cause cancer, while the picture remains a little more hazy regarding sugar substitutes and weight loss, as we previously reported.
Several other experts commented on the "controversial but inconclusive" nature of the association.
Besides this those who drank diet sodas believing that they would be let off the hook thanks to the artificial sweeteners in them were not doing themselves any favors. Sugar has always been associated with obesity, heart disease, and diabetes, he adds, but fewer studies have been done on its long-term effects on the brain.
Now, because this was an observational study-meaning it identifies trends over time-it can't definitely prove that artificial sweeteners somehow cause dementia or stroke.
For its stroke analysis, the seven-year study looked at the beverage intake of 2,888 Framingham Heart Study participants older than 45 years old. Both groups were primarily Caucasian and were just under 50% male.
Researchers then followed the group for 10 years, noting 97 cases of stroke during that period, and 81 cases of dementia (63 cases were specifically Alzheimer's disease).
"Given such small numbers, consumption of low-calorie sweetened beverages could be divided into 3 levels only, i.e. non users, occasional (less than daily) and regular users (one or more beverage per day)". People who drink one can or more diet soda per day are three times more likely to suffer from the conditions, the researchers found.
But even after excluding diabetics from the study, diet soda consumption was still associated with the risk of dementia. The research, which was conducted by Boston's University School of Medicine, has also found a "worrying association" between diet fizzy drinks and Alzheimer's disease.
American researchers have examined the effects of light beverages on health, particularly brain health.
Dr Mary Hannon-Fletcher, the Head of Health Sciences at Ulster University in the United Kingdom, said that although the research was good, the methods of getting the data had limitations.