People who drink at least one artificially sweetened beverage a day could have almost three times the risk of developing dementia or stroke compared with those who drink such beverages less than once a week, according to new research published Thursday in the journal Stroke.

“It was somewhat surprising that diet soda consumption led to these outcomes,” said lead author Matthew Pase, Ph.D., a senior fellow in the Department of Neurology at the Boston University School of Medicine and Swinburne University of Technology in Melbourne, Australia. Previous studies have linked diet soda intake to stroke risk, but the link with dementia was not previously known, he said.

The investigators reached their conclusion after reviewing the beverage consumption habits of 2,888 people who were aged more than 45 years for the stroke arm of the study and 1,484 people aged more than 60 years for the dementia arm. All of the study participants were part of the Framingham Heart Study.

Study participants reported their eating and drinking habits via questionnaires. The researchers then followed up with them for the next 10 years to determine who developed stroke or dementia, then compared the dietary information with the risk of developing stroke and dementia over the course of the study.

Although the study did not find an association between stroke or dementia and the consumption of sugar-sweetened drinks, switching to beverages sweetened with sugar isn’t necessarily better for the brain, Pase said.

“We recommend that people drink water on a regular basis instead of sugary or artificially sweetened beverages,” he said.

A separate study published March 5 in the journal Alzheimer’s & Dementia, also with Pase as the first author and using data from the Framingham Heart Study, found that people who drank more than three sodas a week or consumed two sugary drinks a day of any type — soda, fruit juice and other soft drinks — had multiple signs of accelerated brain aging. These signs included smaller overall brain volume, poorer episodic memory and a shrunken hippocampus, all risk factors for early-stage Alzheimer’s disease. The investigators also found that drinking at least one diet soda per day was associated with smaller brain volume.

“It looks like there is not very much of an upside to having sugary drinks, and substituting the sugar with artificial sweeteners doesn’t seem to help,” said Sudha Seshadri, a professor of neurology at Boston University School of Medicine and a faculty member at the university’s Alzheimer’s Disease Center. She was the senior author on both papers.

“Maybe good old-fashioned water is something we need to get used to,” Seshadri added.

The findings of both studies demonstrate correlation but not cause and effect, the researchers stressed. They cautioned against over-consuming any type of sugar-sweetened or artificially beverage but said more research is needed to determine how — or if — the drinks actually damage the brain.