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Is Soda Bad for Your Brain? (And Is Diet Soda Worse?)

MED researchers’ studies: both correlated with accelerated brain aging

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Americans love sugar. Together we consumed nearly 11 million metric tons of it in 2016, according to the US Department of Agriculture, much of it in the form of sugar-sweetened beverages like sports drinks and soda.

Now, new research suggests that excess sugar—especially the fructose in sugary drinks—might damage your brain. Researchers using data from the Framingham Heart Study (FHS) found that people who drink sugary beverages frequently are more likely to have poorer memory, smaller overall brain volume, and a significantly smaller hippocampus—an area of the brain important for learning and memory. The FHS is the nation’s longest running epidemiological study, begun in 1948, supported by the National Heart, Lung, and Blood Institute, and run by BU since 1971.

But before you chuck your sweet tea and reach for a diet soda, there’s more: a follow-up study found that people who drank diet soda daily were almost three times as likely to develop stroke and dementia when compared to those who did not.

Researchers are quick to point out that these findings, which appear separately in the journals Alzheimer’s & Dementia and Stroke, demonstrate correlation but not cause and effect. While researchers caution against overconsuming either diet soda or sugary drinks, more research is needed to determine how—or if—these drinks actually damage the brain, and how much damage may be caused by underlying vascular disease or diabetes.

“These studies are not the be-all and end-all, but it’s strong data and a very strong suggestion,” says Sudha Seshadri, a School of Medicine professor of neurology and a faculty member at BU’s Alzheimer’s Disease Center, senior author on both papers. “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.”

Matthew Pase, Framingham Heart Study investigator

Matthew Pase is lead author on two studies that link higher consumption of both sugary and artificially sweetened drinks to adverse brain effects. Photo by Cydney Scott

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

Matthew Pase, a fellow in the MED neurology department and an FHS investigator, who is lead author on both papers, says that excess sugar has long been associated with cardiovascular and metabolic diseases like obesity, heart disease, and type 2 diabetes, but little is known about its long-term effects on the human brain. He chose to study sugary drinks as a way of examining overall sugar consumption. “It’s difficult to measure overall sugar intake in the diet,” he says, “so we used sugary beverages as a proxy.”

For the first study, published in Alzheimer’s & Dementia on March 5, 2017, researchers examined data, including magnetic resonance imaging (MRI) scans and cognitive testing results, from about 4,000 people enrolled in the FHS Offspring and Third-Generation cohorts. (These are the children and grandchildren of the original volunteers enrolled in 1948.) The researchers looked at people who consumed more than two sugary drinks a day of any type—soda, fruit juice, and other soft drinks—or more than three per week of soda alone. Among that high-intake group, they found multiple signs of accelerated brain aging, including smaller overall brain volume, poorer episodic memory, and a shrunken hippocampus, all risk factors for early-stage Alzheimer’s disease. Researchers also found that higher intake of diet soda—at least one per day—was associated with smaller brain volume.

In the second study, published in Stroke on April 20, 2017, the researchers, using data only from the older Offspring cohort, looked specifically at whether participants had suffered a stroke or been diagnosed with dementia because of Alzheimer’s disease. After measuring volunteers’ beverage intake at three points over 7 years, the researchers then monitored the volunteers for 10 years, looking for evidence of stroke in 2,888 people over age 45, and dementia in 1,484 participants over age 60. They found, surprisingly, no correlation between sugary beverage intake and stroke or dementia. However, they found that people who drank at least one diet soda per day were almost three times as likely to develop stroke and dementia.

Although the researchers took age, smoking, diet quality, and other factors into account, they could not completely control for preexisting conditions like diabetes, which may have developed over the course of the study and is a known risk factor for dementia. Diabetics, as a group, drink more diet soda on average, as a way to limit their sugar consumption, and some of the correlation between diet soda intake and dementia may be due to diabetes, as well as other vascular risk factors. However, such preexisting conditions cannot wholly explain the new findings.

“It was somewhat surprising that diet soda consumption led to these outcomes,” says Pase, noting that while prior studies have linked diet soda intake to stroke risk, the link with dementia was not previously known. He adds that the studies did not differentiate between types of artificial sweeteners and did not account for other possible sources of artificial sweeteners. He says that scientists have put forth various hypotheses about how artificial sweeteners may cause harm, from transforming gut bacteria to altering the brain’s perception of sweet, but “we need more work to figure out the underlying mechanisms.”

8 Comments
Barbara Moran, Senior Science Writer
Barbara Moran

Barbara Moran can be reached at bmoran@bu.edu.

8 Comments on Is Soda Bad for Your Brain? (And Is Diet Soda Worse?)

  • D. Ketten on 04.21.2017 at 7:57 am

    Interesting article and valuable research. This article focuses on soda, which raises some questions. As noted, fructose is a common sweetener, and therefore it is good that fruit juices were included in the study, but it does not indicate whether the analyses showed the same outcomes. Also, did the analyses reveal whether there were differences or equivalent trends for sucrose based drinks? Similarly, did they do a control study of potential effects of simple carbonation; i.e., plain soda water, club soda, unflavoured sparkling water consumption?

    • Matthew on 04.23.2017 at 7:06 am

      Higher intake of fruit juice was associated with smaller overall brain volumes, smaller hippocampal volumes (specific area of the brain important for memory) and poorer memory performance. Intake of fruit juices combined with sugary soda was not associated with the risk of stroke or dementia in our second study.

      Based on the nature of the data that we collected, we were unable to differentiate between different sugars or different sweeteners used in soda. We also did not consider the effects of carbonation alone. As you point out, there are still many questions that require further investigation.

  • Kunal Patel on 04.21.2017 at 10:09 am

    Very interesting research and information there. But also need more research on effect of coloring agents (Dyes, made from the same petroleum that fuels our vehicles) added to drinks and other foods.

  • Tochukwu on 04.22.2017 at 7:28 am

    We the rate at which sugar is been consumed, diabetes will no longer be an illness for the old.
    I have seen little children less than age 15 with serious diabetes.
    Lets try and reduce our intake of sugar.
    And more grease to barbara’s elbow, for writing such a wonderful article.

  • Matthew on 04.23.2017 at 7:11 am

    Thank you Kunal for your comment. Based on the nature of our data, it was not possible to examine these factors. Experimental studies will be needed to test the effects of coloring agents and other additives on health. As you point out, there are many questions remaining for future research.

  • Katy on 04.24.2017 at 11:10 am

    I know this is a much harder question, but are there any thoughts on how/why these sweeteners lead to brain disease/disorders?

    Thanks for sharing this research. Periodic reminders about the risks of sugar always help me keep my soda consumption down :)

  • Jim in New Orleans on 04.24.2017 at 10:06 pm

    One key thing to keep in mind with this study is that the “three times as likely to develop stroke and dementia when compared to those who did not” data represents relative risk. And here is a quote from the news release by co-author Matthew Pase, MD that’s oft-omitted:

    “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.”

    Of course, at 58-years-old and one who drinks a Coke 0 per day, I may be pointing this out to alleviate my own concerns about one day developing some form of dementia. Also, I don’t see other risk factors such as heredity and the part it played mentioned in the article. I know my own parents gobbled down artificial sweeteners by the barrel, but neither one of them developed dementia and lived to a ripe old age (early 90s); however, they both had cardiovascular diseases.

    The report indicates some cause for concern, but not necessarily causality. Nevertheless, if it convinces folks to indeed gravitate toward good old fashioned water, then so much the better.

  • Alventis Gravely on 07.20.2017 at 2:24 pm

    I drank diet sodas when I became a diabetic then I begin to have bad leg cramps I finally prayed and ask God what was causing my cramps they were very very bad. He said stop drinking those diet sodas and I did. No more cramps thank God.

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