New York: When it comes to the dangers of regularly drinking soda and other sugar-sweetened beverages, the science is clear. It rots your teeth, makes you fat, and puts you at a higher risk of diabetes, heart attack, and stroke. The list goes on and on—just ask your doctor.
When it comes to diet soda, the science has been less solid. It will lower your overall sugar consumption to switch from Coke to Diet Coke, but it might cause other problems. Artificial sweeteners have been associated with—but not shown to necessarily cause—weight gain, diabetes, and heart disease.
On Thursday, two studies by the same group of researchers gave soda drinkers—both diet and regular—a whole new reason to drop their habit entirely.
The first, published in the medical journal Stroke, found that consumption of artificially sweetened beverages was associated with a higher risk of stroke and dementia, including Alzheimer’s disease. The second, published in Alzheimer’s & Dementia, found that higher consumption of sugary beverages was associated with markers for pre-clinical Alzheimer’s disease.
Led by researchers at Boston University School of Medicine, the Stroke study authors conducted a review of data collected through the Framingham Heart Study, a multi-decade observational review that began with more than 5,000 volunteer participants in 1948, and has also included their offspring since 1971, and their grandchildren since 2002. The FHS entailed nine examination cycles approximately every four years—participants logged their beverage intake through questionnaires that surveyed their diets over the previous 12 months. In these studies, the researchers looked at the seventh cycle for the offspring, between 1998 and 2001, and the second cycle for the grandchildren, from 2008 to 2011.
In the Alzheimer’s & Dementia study, the researchers found that higher consumption of sugary beverages was associated with a pattern consistent with preclinical Alzheimer’s, including smaller total brain volume and poorer episodic memory. The authors called the findings “striking” because they were found in a middle-aged sample and remained even after statistical adjustment for factors like physical activity and total caloric intake. The results align with earlier research done with smaller samples, including among 737 middle-aged participants in the Boston Puerto Rican Health Study, which found higher sugar intake was cross-sectionally associated with Alzheimer’s-like behavioural patterns.
The study notes its limitations, including that it doesn’t establish causality, the homogenous population sample didn’t include minorities, and the inherent unreliability of a questionnaire based consumption data.
In response, William Dermody Jr., vice president of policy at the American Beverage Association, the chief lobby for soda makers, noted “The Alzheimer’s Association points out that the greatest risk factors for Alzheimer’s are increasing age, family history of Alzheimer’s, and genetics—not sugar intake, from any source.”
The Stroke study, meanwhile, found an association with artificially sweetened beverages and stroke and dementia, while not finding a similar association for consumption of sugar-sweetened beverages, an observation the authors characterized as “intriguing.” An editorial accompanying the study noted this finding—and that it contradicted other studies that found the opposite. This study, the authors note, has the same limitations as the Alzheimer’s & Disease analysis, as well as another important one: This association could be a case of reverse causality, “whereby sicker individuals consume diet beverages as a means of negating a further deterioration of health.”
That concern is based on the way diabetes status partially mediated the association between artificially sweetened beverage consumption and dementia. In other words, having diabetes may be more of a risk factor for dementia than consuming artificially sweetened beverages is. The relationship between beverage consumption, diabetes, and dementia remains unclear.
All of this, says Dean M. Hartley, director of Science Initiatives at the Alzheimer’s Association, points to an important reminder: Correlation doesn’t necessarily mean causation. Dermody of the American Beverage Association emphasized this point: “The authors of this study acknowledge that their conclusions do not—and cannot—prove cause and effect.”
Still, Hartley said, this study provides an important starting point for further studies. “Many of our first understandings of a disease come from associations,” he says. “It’s why it’s critical to get more funding at a national level.” The Alzheimer’s Association has been advocating for increased research funding, including a $400 million boost for 2017 through the National Institutes of Health, currently pending before Congress, and at least another $414 million for 2018. (The Trump administration budget proposal calls for a $5.8 billion cut to the NIH for 2018.)
Hartley also recommends the Association’s 10 Ways to Love Your Brain for proactive steps towards brain health, including exercise, a healthy diet, and keeping up your education, and advises everyone to speak with their physician about their specific health conditions. Still, when it comes to soda, diet or regular, the safest course is to skip it. “I think they’re both bad,” he says. “Pure water is always a very good thing.” Bloomberg