Although the scientists could not find a link between sugary drinks and either of the illnesses, they are now saying that diet drinks should not be regarded as a healthy alternative.
The researchers acknowledged several study limitations, including the observational nature of the data, the absence of ethnic minorities, and the use of a self-reported questionnaire to obtain dietary intake data, which may be subject to recall bias.
"The sample sizes are different because we studied people of different ages", Pase said. Similarly, dementia is rare in people younger than 60 years old.
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).
Researchers found that drinking diet soda daily raises a person's risk of dementia and a stroke by three times, compared to those who drink less than one diet soda a week, USA Today reports. They were also almost three times as likely to receive an Alzheimer's diagnosis, too. "We recommend that people drink water on a regular basis instead of sugary or artificially sweetened beverages", said Mr Pase.
In an editorial accompanying the Stroke study, neurologists from the University of Miami and the University of Munster in Germany write that current research is inconclusive about whether diet beverages actually contribute to an increased risk of stroke, dementia, diabetes, and metabolic syndrome.
Daily consumption of "diet" drinks containing synthetic sweeteners may be linked to an increased risk of stroke or suffering from dementia, according to a U.S. study.
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As our readership is well aware, low-calorie sweeteners have been extensively reviewed by government safety authorities around the world, including the U.S. Food and Drug Administration (FDA), and proven to be safe for consumption.
While these findings might cause concern, researchers clarified that this study is purely observational and can not prove that artificially sweetened beverages definitely cause dementia or stroke. For lower consumption (between 1 and 6 drinks per week), the risk is increased by an ischemic stroke (2.6 times more risk), but not to develop dementia. Pase believes this is the first study to look at its association with risk of dementia and he hopes the work will spur more research into the effects of these sweeteners on the brain.
"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", Seshadri, who is senior author on both papers, said.
The authors caution that, while their studies were large and lengthy, they don't prove that soft drinks lead to memory or brain problems; they only found links between the drinks and brain effects.
"This included a higher risk of ischemic stroke, where blood vessels in the brain become obstructed and Alzheimer's disease dementia, the most common form of dementia".
The two studies must be taken as warning signs, Keith Fargo, Ph.D., director of scientific programs and outreach at the Alzheimer's Association, said. Artificial sweeteners may have effects in the body that we havent begun to explore..
She also questioned whether the data was sound. These are recommendations from the Alzheimer's Associations list of 10 lifestyle habits to reduce risk of cognitive decline.