Soda lovers won’t be sweet on these new health studies.

A pair of new reports drawn from the Framingham Heart Study (FHS) at Boston University Medical Center link sipping sugary drinks with poor memory and smaller brain volume. Worse, they tie a daily diet soda habit to a much higher risk of suffering stroke and dementia.

In the first study, researchers analyzed 4,000 people enrolled in the heart study over the age of 30, and used MRI scans and cognitive tests to measure any relationship between sweetened beverage intake and neurological health markers like brain volumes, thinking and memory. Americans swallowed 11 million metric tons of sugar last year, according to the U.S. Department of Agriculture, so lead author Matthew Pase and his team were curious about what the sweet stuff does to the brain.

They found a correlation – although not a direct cause-and-effect just yet – between people who drink more than two or three sweetened beverages like soda, juice and sports drinks a day (or more than three sodas a week alone) and signs of accelerated brain aging. These adverse effects included smaller overall brain volume, poorer episodic memory and a shrunken hippocampus (also important for memory), which can be risk factors for early-stage Alzheimer’s disease. And gulping one diet soda a day was also associated with smaller brain volume.

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)

The news gets worse for diet drink lovers. The second follow-up study spent a decade monitoring 2,888 participants age 45 and up for any stroke development, and 1,484 participants age 60 and up for dementia due to Alzheimer’s, while measuring their beverage intake at three points over seven years. While they found no correlation between sugary drinks overall and stroke or dementia, they did find that people who drank at least one diet soda a day (typically mixed with artificial sweeteners) were almost three times more likely to develop stroke and dementia than those who didn’t drink diet soda.

“It was somewhat surprising that diet soda consumption led to these outcomes,” lead author Pase said in his report, noting that they did not differentiate between sugar and artificial sweeteners in this study, so “we need more work to figure out underlying mechanisms.”

Diabetes is a risk factor for dementia, and diabetics often drink more diet soda on average to limit their sugar intake, which could account for some of the correlation between diet drinks and dementia. But even after excluding diabetics, sipping diet soda was still associated with higher rates of dementia.

Reps from two of the biggest sweetened beverage makers, Coca Cola Company and PepsiCo, who were contacted for comment on the reports, referred Moneyish to the American Beverage Association. The ABA responded with, “Low-calorie sweeteners have been proven safe by worldwide government safety authorities as well as hundreds of scientific studies and there is nothing in this research that counters this well-established fact,” noting that, “The FDA, World Health Organization, European Food Safety Authority and others have extensively reviewed low-calorie sweeteners and have all reached the same conclusion – they are safe for consumption.”

The ABA also emphasized that the new studies acknowledge they don’t prove cause and effect. “According to the National Institutes of Health (NIH), many risk factors can increase an individual’s likelihood of developing stroke and dementia including age, hypertension, diabetes and genetics,” it added. “NIH does not mention zero calorie sweeteners as a risk factor.”

The studies’ senior author Sudha Seshadri, a professor of neurology at Boston University School of Medicine, admitted the reports “are not the be-all and end-all, but it’s strong data and a very strong suggestion.

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