Many Americans continue to consume sugary beverages, such as soda, even though it can lead to weight gain and other adverse health events. The US Department of Agriculture reported than in 2016, Americans consumed 11 metric tons of sugar, with a majority derived from sports drinks and sodas.
 
Excess sugar, particularly from beverages, may damage the brain, according to 2 new studies published by Alzheimer’s & Dementia and Stroke. The authors found that individuals who drank sugary beverages were more likely to have poor memory, smaller brain volume, and a smaller hippocampus.
 
A follow-up analysis revealed that individuals who consumed diet soda were 3 times more likely to experience a stroke and develop dementia compared with those who did not consume these beverages. This suggests that diet soda may not truly be a healthier alternative to regular soda.
 
"These studies are not the be-all and end-all, but it's strong data and a very strong suggestion," said senior study author Sudha Seshadri, MD. "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. Maybe good old-fashioned water is something we need to get used to.”
 
Excess sugar intake has previously been linked to cardiovascular and metabolic diseases, but the long-term effects are unknown, according to the study. The authors chose to determine overall sugar intake through consumption of sugary drinks.
 
"It's difficult to measure overall sugar intake in the diet, so we used sugary beverages as a proxy,” said corresponding author Matthew Pase, PhD.
 
Included in the Alzheimer’s & Dementia study were 4000 individuals who were enrolled in the Framingham Heart Study’s Offspring and Third-Generation cohorts. Patients included consumed more than 2 sugary drinks per day – soda, fruit juice, soft drinks – or more than 3 sodas per week. The authors examined data, such as MRI scans and cognitive test results, for each patient.
 
Patients who consumed high volumes of sugary drinks were found to have signs of accelerated brain aging, which were all risk factors for early Alzheimer’s disease, according to the study. Consuming at least 1 diet soda per day was also linked to reduced brain volume.
 
In the second study, published by Stroke, the authors examined whether participants had experienced a stroke or developed Alzheimer’s disease-related dementia. Participants’ beverage consumption was measured 3 times over 7 years. These individuals were monitored for 10 years.
 
The authors examined evidence of stroke among 2888 patients over age 45 and dementia in 1484 patients over age 60. They found no link between sugary beverage intake and the conditions; however, individuals who drank 1 or more diet sodas per day were nearly 3 times as likely to experience stroke or develop dementia, according to the study.
 
The authors accounted for age, smoking, diet, and other factors, but they did not fully control for conditions – such as diabetes – that may have developed during the studies. Preexisting conditions were not observed to be wholly responsible for the new findings, according to the study.
 
"It was somewhat surprising that diet soda consumption led to these outcomes," Dr Pase said.
 
The link between diet soda intake and stroke risk was previously discovered, but the link to dementia was not unknown, according to the study.
 
The authors noted that while the results show a correlation, it does not indicate cause-and-effect, according to the study. More research is required to determine how sugary drinks can damage the brain and if the damage stems from vascular disease or diabetes. In the meantime, the authors caution against consuming large amounts of diet soda and sugary drinks.
 
The current studies did not make a determination between different types of artificial sweeteners and did not account for other sources of the sweeteners, according to the authors.  Other studies have shown that the sweeteners may alter gut bacteria or the brain’s perception, but additional studies are needed.
 
"We need more work to figure out the underlying mechanisms,” Dr Pase concluded.