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Two new studies suggest that both sugar- and artificially sweetened drinks might have negative effects on the brain.

Amanda MacMillan
April 21, 2017

People who drink soda and sugary juices on a regular basis have smaller brains and accelerated signs of brain aging, according to a recent study. But artificially sweetened beverages may not be any better for your mind: In a second study, people who drank diet soda every day were there times as likely to have a stroke or develop dementia than those who didn’t.

In other words, there’s not much of an upside to drinking sugary sodas—and swapping them for artificial sweeteners doesn’t seem to help. The new research can’t prove a cause-and-effect relationship between drinking habits and health effects, but it does strongly suggest a connection, says Matthew Pase, PhD, a neurology fellow at Boston University School of Medicine and contributing author on both new papers.

The first study, published last month in Alzheimer’s & Dementia, analyzed food questionnaires, MRI scans, and cognitive exams of about 4,000 people ages 30 and up.In this group, researchers found that people who consumed more than three sodas per week—or more than two sugary drinks of any type (soda, fruit juice, and other soft drinks) per day—were more likely to have memory problems, a smaller brain volume, and a smaller hippocampus (an area of the brain used in learning and memory). Drinking at least one diet soda a day was associated with smaller brain volume, as well.

In the second study, published yesterday in the journal Stroke, the researchers followed two different groups of adults for 10 years. Out of nearly 3,000 adults over age 45, 97 suffered a stroke during that time. And out of nearly 1,500 adults over 60, 81 developed Alzheimer’s disease or another form of dementia.

The researchers found no correlation between sugary beverage intake and either health condition. “This was a little surprising, because previous studies have found associations between high intake of sugary beverages and higher risk of stroke,” says Pase. Sugar has long been associated with obesity, heart disease, and diabetes, he adds, but fewer studies have been done on its long-term effects on the brain.

They did find a link, however, between health outcomes and artificially sweetened beverages: People who’d reported drinking at least one diet soda per day were three times as likely to have had a stroke, and 2.9 times as likely to have developed dementia. (The studies did not differentiate between types of artificial sweeteners.)

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Previous studies have linked diet sodas to an increased risk of weight gain and stroke, and scientists have hypothesized that artificial sweeteners may affect the body in several different ways—from transforming gut bacteria to tricking the brain into craving more calories. This is the first time diet sodas have been linked to dementia—although it’s not that surprising, says Pase, since stroke is a risk factor.

The analysis adjusted for factors such as age, smoking status, diet quality, and education. But it wasn’t able to control completely for conditions like diabetes, which may have developed over the course of the study.

Because diabetics drink more diet soda than the general population, the authors say that the disease may partially explain the increase in dementia rates—but not completely. When diabetics were excluded from the calculations, the association still remained.

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According to the United States Department of Agriculture, Americans consumed nearly 11 million metric tons of sugar in 2016, much of it in the form of sweetened beverages. Pase says the studies focused specifically on beverages because it would be difficult to measure total sugar intake from all different food sources.

If you have been a soda drinker, that doesn’t mean you should panic. “This is by no means a certain fate," says Pase. He points out that only 3% and 5% of people in the study had a stroke and developed dementia, respectively, so the overall numbers are still small.

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.

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But a growing number of studies suggest that they may not be a safe alternative to sugary drinks, they add, and more research is highly encouraged. “Even small causal effects would have tremendous effects on public health,” they write, given the popularity of both regular and diet sodas. They conclude that both sugar- and artificially sweetened soft drinks “may be hard on the brain.”

Pase agrees that, until more is known, it’s smart to limit both types of soft drinks. “We know that sodas have no real nutritional value, so it’s not that strange to say we should be cautious about consuming them in excess,” he says. “I think water is the best choice.”