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

Both sugary and diet drinks correlated with accelerated brain aging

New research correlates sugary drinks—as well as diet soda—to smaller brain volume and memory deficits. Photo by RapidEye/iStock

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.

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 over-consuming 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 professor of neurology at Boston University School of Medicine (MED) and a faculty member at BU’s Alzheimer’s Disease Center, who is 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 investigator at the FHS 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 Framingham Heart Study’s Offspring and Third-Generation cohorts. (These are the children and grandchildren of the original FHS 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 due to Alzheimer’s disease. After measuring volunteers’ beverage intake at three points over seven 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. Here 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.”

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17 comments

  1. More obese and unfit people drink diet drinks. It’s more likely that the correlation is linked to their state of health – the reason why they;re consuming the drink you’re suspicious of. Take the same data and now look at weight (height to waist ratio) and frequency of exercise. The link will likely be revealed as lazy/obese/unfit people.

    1. People with a smaller hippocampus and overall brain volume might be more likely to ignore healthy diet and exercise advice, involving dedication and work; and supplement their poor diet and low exercise lifestyle with diet drinks, diet pills and infomercial machines that claim to do exercise for you. As stated above, the correlations found could simply be indicative of people likely to have such conditions being attracted to the drinks and not the conditions relating to the consumption of the drinks themselves.

    2. Thank you for your comment. It is possible that those who are unfit or obese gravitate more towards diet beverages. To explore this, we adjusted our results for physical activity. We found that the observed findings exist even once you take physical activity into account. Our findings also did not appear to be explained by waist to hip ratio.

  2. I’m curious if there was any distinction between saccharine, aspartame and sucralose? Sodas have varied over the years.

    1. Hi there – good question. The studies did not differentiate between types of artificial sweeteners and did not account for other possible sources of artificial sweeteners.

    2. Actually, they studied soda consumption between 1991 and 2001 when I’m pretty sure NO sodas were sweetened with sucralose, then did 10 years of follow-up. So it had to be all saccharine and aspartame.

  3. Drank diet coke all my life. At one point a case a day which is documented!Had a stroke and have dementia. Sometimes can not remember my grand childrens names. Is there any help for this?

  4. This is a big wake up call. I drink 2 Liters (!) of Pepsi Max a day. But I must stop! Thanks for this research and your hard work.

  5. When considering diet quality was electrolyte intake a factor? Considering the small brain mass this sounds like a electrolyte disorder such as hypernatremia.

  6. Did the study include people who stopped drinking or significantly reduced diet soda intake which correlated to reduced level of stroke in latter years?

  7. It would be intresting to see research on the other “Secret” ingredients in soft drinks. We all have our eyes set on sugar vs artificiall sweeteners. isnt it posible that the other stuff within these drinks can cause these symptoms?

    1. I have a similar question. I do not doubt the damage that is possible from high sugar intake or high artificial sweetener intake but what about the active ingredients in products such as coke and Pepsi?

  8. The reason for the brain effect detected in this study could be the aluminium container/can used for the soft drink. Normally, we are exposed to aluminium (Al) protected with an “insoluble” oxide surface layer. However, when the can is opened, there will be an edge with fresh Al the liquid passes, and some Al will be dissolved in the acidic liquid. If soluble aluminium reaches the brain, it can induce Alzheimer-like brain damage. We know that a. o. because some dialysis patients 40 years ago died or got brain damage, because Al hydroxide then was used to “clean” the dialysis water. The healthy kidney has a good ability to excrete surplus of aluminium from the body but nowadays more and more people have decreased kidney function.
    The CNS toxicity of “soluble” aluminium may also be the explanations for some side effects of vaccinations using vaccines with aluminium hydroxide based adjuvants.

  9. Interesting to see that artificial sweetener can cause dementia. I have a niece with PKU who cannot EVER ingest any form of aspartame due to the dual strand of phenylalanine. An untreated person with PKU develops mental retardation and finally death due to the build up of Phenylalanine as Phenyl Pyruvic acid. Has anyone looked to see if the people with mental retardation from untreated PKU have the same plaques? Could dementia be treated the same way PKU is treated? Low Protein diet and Kuvan?

  10. Over thirty years ago, Doctor Adrian Gross, testified before Congress that animals given aspartame in experiments developed tumors. Diet sodas have a substance that is called diketopiperazine which is a brain tumor agent. Aspartame has methanol which can break down into formaldehyde which can actually harm DNA. It should be surprising to no one, the potential devastation that diet sodas can do to your brain. for more information go to Doctor Mercola’s site

  11. I have consumed 3 to 4 litres of Pepsi Max per day since the mid 90’s. Friends and work colleagues have considered me a barometer of any bad effects as a warning for their more moderate consumption. No strokes due to my thin blood (hereditary family condition) and no dementia as yet. I considered the stroke risk as mentioned from an earlier study as low risk for me. However I do not find that the aluminium can to be a plausible theory as the comparison was to sugar soda drinkers (prevelance of can use the same). The comparison also strikes out the theory of an artificial coloring culprit from can allowed to get hot (as incidents should be similar).
    I am now concerned as my generous endowment of little grey cells is now at risk from a lone asassin in a crowd and no-one can identify him ? I am avoiding crowds until I can resolve the matter. Without my old stimulant sidekick this may be more difficult.

  12. Can the study data be divided into people who consume sugar from other sources and those who do not consume sugar from other sources? It seems to me that the old joke about the guy who orders the banana split but wants a diet coke to go with it could be operative here.

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