So you thought you'd live life to the max and reduce your sugar intake to zero by switching to diet fizzy drinks? If only it were that simple.

New research is hinting that what might be good for your waist-line just might pose a problem for your brain later.

As part of a series of investigations into how sweet carbonated drinks affect our brains, Boston University School of Medicine used surveys to identify any long term neurological effects of consuming drinks artificially sweetened with substances such as aspartame or saccharine.

Participants were taken from the long-term Framingham Heart Study Offspring cohort – a group of about 5,000 men and women who have volunteered to provide data over their lifetime since 1971.

The team studied 2,888 members of the cohort aged over 45 for signs of a stroke, and found 97 cases (of which 87 were clots that restricted blood flow, called ischemic strokes).

A total of 81 cases of dementia were found among 1,484 members aged over 60 were, with 63 of those having symptoms consistent with Alzheimer's disease.

They then used questionnaires that the participants had filled out at several points in their life over a seven year period to determine their food intake.

Crunching the numbers and accounting for factors such as age, education, caloric intake, smoking, and exercise, it appears throwing back at least one diet soda a day makes it nearly three times more likely you'll have an ischemic stroke – a condition that can cause dementia – or develop Alzheimer's.

On the other hand, a parallel study failed to find evidence that drinking sugary drinks increased the risk of stroke or dementia at all.

Before you run to the fridge and pour several litres of Pepsi Max down the sink, it's important to put all of this into perspective.

First of all, three times a really tiny risk is still a tiny risk.

"In our study, three percent of the people had a new stroke and five percent developed dementia, so we're still talking about a small number of people developing either stroke or dementia," said the study's lead researcher, Matthew Pase.

And of course there is the all-important mantra 'correlation isn't causation'. While the statistics suggest something could be going on, it doesn't necessarily draw a straight line from sweetener to stroke.

The survey was also limited to data that had already been collected as a part of the Framingham Heart Study, which was made up of people from a mostly Caucasian ethnic background.

Culture could therefore be hiding some important details, especially given the differences in sugary drinks consumed across demographics, the researchers note.

There also was no indication of whether a specific artificial sweetener was to blame given participants didn't note down the variety of beverage consumed.

But with public health messages encouraging people to lose weight, it might be worth considering the potential impact of more people drinking sugar-free if it isn't completely risk-free.

"Our study shows a need to put more research into this area given how often people drink artificially-sweetened beverages," said Pase.

The American Beverage Association is keen to take the results with a grain of non-sweetened salt.

"Low-calorie sweeteners have been proven safe by worldwide government safety authorities as well as hundreds of scientific studies and there is nothing in this research that counters this well-established fact," it said in a statement.

"The FDA, World Health Organization, European Food Safety Authority and others have extensively reviewed low-calorie sweeteners and have all reached the same conclusion – they are safe for consumption." 

More research is always a good thing. But we all like to know what this means for us now, without holding out for the next round of grants. 

The best solution might just be to swap soft drinks for water or drinks without added sweeteners as much as possible.

"They may have a role for people with diabetes and in weight loss, but we encourage people to drink water, low-fat milk or other beverages without added sweeteners," said professor of nutrition at the University of Vermont, Rachel K. Johnson.


This research was published in the journal Stroke.