Published on: April 25, 2017
by Alice G. Walton for Forbes:
The sugar-brain connection isn’t just a theory anymore. There’s some fairly convincing and reproducible evidence that too much sugar in the diet is linked to cognitive and brain deficits. Two new papers, both deriving data from the long-running Framingham Heart Study, bear this out. One study finds that sugary drinks are linked to pre-clinical Alzheimer’s disease: Poor memory and reduced brain volume in certain areas. The other study finds that artificial sweeteners aren’t much better—they’re linked to a greater risk of stroke and of dementia. So it seems like we’re damned if we do and damned if we don’t, at least when it comes to sweetened drinks.
The first of the studies, from Boston University School of Medicine, followed more than 4,200 people, periodically testing them for memory and cognition, and scanning their brains with MRI to measure volume. The participants also filled out questionnaires about their food intake, including sugary drink consumption (including both soda and fruit juices). Sugary drinks are a great way to study excess sugar, since they have almost no redeeming nutritional qualities, like protein or fiber to slow their absorption—it’s like a straight drug to the system.
It turned out that people who consumed more sweetened drinks had poorer memory and reduced overall brain volume (particularly in the hippocampus, the area that’s known to “house” short-term memory), compared to people who didn’t drink sugary drinks.
In fact, the authors calculated that one to two sugary drinks per day was associated with 1.6 years of brain aging; more than two drinks per day was associated with two extra years of aging. For memory, the association was even more pronounced: One to two, and greater than two, sugary drinks per day corresponded to 5.8 and 11 years of brain aging, respectively.
The other study, also using data from the Framingham participants, looked at the link between sugary drink consumption, artificially sweetened drink consumption and dementia and stroke. It didn’t find a link between sugary drinks and dementia or stroke, but it did find a link between artificially sweetened drink consumption and both types of brain disease. In fact, participants who drank at least one artificially sweetened drink per day were three times as likely to develop stroke and almost three times as likely to develop Alzheimer’s disease.
Why didn’t the second study find a link between sugar and brain disease, as the first one did? “There are a number of possible reasons,” says study author Matthew Pase. “One is that in our sample, people didn’t frequently consume regular soda—more drank diet drinks. So it’s possible we were underpowered since sugary drinks just weren’t that widely consumed.” The other point he makes is that the people who often consumed sugary beverages were at risk of other diseases—so they may not have had time to develop the brain diseases that were being tested for.
Despite the lack of sugar-brain disease connection in the second study, Pase says he strongly believes in the connection between sugar and brain disease, given the results of his first one, and the fast-growing body of other work that’s illuminating the connection. “We know that sugar beverages and excess sugar are associated with metabolic disease,” he says. “The brain relies on a steady flow of blood. Metabolic and vascular diseases don’t just happen in the body—they happen in the brain, too.” Earlier work has shown in both mice and humans that impaired glucose function is linked not only to cognitive deficits but also to the patterns of protein dysfunction (amyloid-beta and tau) that are associated with Alzheimer’s disease.
Why artificial sweetener consumption would be linked to brain disease is another question. Reverse causation could be a factor, whereby people with already-existing health problems are more likely to drink artificially sweetened drinks in an effort to be healthier—for instance people who already have diabetes are more likely to switch to diet drinks as a result, and they’re also more likely to develop dementia. Or it could be that diet drinks screw up the brain’s feedback system, so people unwittingly seek out sugar elsewhere. Artificial sweetener has also been shown to tweak one’s gut bacteria, the disruption of which can be linked to glucose intolerance and metabolic disease.
The bottom line is that sugar is just as bad for the brain as it is for other organs, maybe worse. Considering that the brain is charged with a lot of critical processes, especially the ones that make us who we are—memory, empathy, emotion—it’s not a good idea to mess with it by consuming the wrong things. After researchers figured out that sugar isn’t healthy, we switched to artificial sweetener—now we know that it’s not without its own risks. Until science figures out a safe way to sweeten liquids, it might be that water, coffee and tea are the only smart options.
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