A diet soda study just found a link with dementia risk. Here’s why you should be skeptical.

This is an article published in the journal Stroke:

A new study published in the journal Stroke shows a correlation between regularly consuming artificially sweetened beverages and stroke and dementia—but experts caution that the study does not show diet soda causes those conditions.

For the study, researchers examined thousands of participants in the long-running Framingham Heart Study. The researchers estimated participants’ artificially sweetened and sugar-sweetened beverage intake based on diet questionnaires completed between 1991 and 2001. The researchers then tracked the incidence of stroke and dementia over a 10-year period beginning in 1998. Specifically, the study tracked:

  • Stroke incidence among 2,888 participates older than 45 years; and
  • Dementia incidence among 1,484 participants older than 60 years.

The researchers then measured the association between drinking at least one artificially sweetened drink a day and the risk of stroke and dementia. The researchers controlled for age, sex, education, caloric intake, diet, physical activity, and smoking.

Study findings

The researchers found drinking artificially sweetened drinks was associated with a higher risk of stroke or dementia—though the absolute number of people who experienced such events was low, at just 58 out of 2,137 participants and 47 out of 1,087 participants, respectively.

The researchers found that the relative incidence of ischemic stroke among participants who drank artificially sweetened beverages at least once per day was 2.96 compared with the rate among participants who drank no more than one such drink a week. The relative incidence of dementia was 2.89 times as high for regular diet beverage drinkers, according to the study.

The researchers said they did not find any association between sugar-sweetened drinks and incidences of either condition. However, a range of experts stressed that such beverages are strongly linked to many serious health issues—such as diabetes—and that the study should not be interpreted in any way as encouraging the consumption of sugary drinks over diet beverages.

Christopher Gardner, director of Nutrition Studies at the Stanford Prevention Research Center, said in an American Heart Association (AHA) release that the takeaway is, “Have more water and have less diet soda, and don’t switch to real soda.”

Some experts question study methodology

Some experts voiced concern about how some media outlets covered the study, cautioning that the study findings did not find a direct cause and effect relationship between artificially sweetened beverages and incidences stroke and dementia. According to Fortune, certain news outlets ran coverage of the study with potentially alarming headlines, such as the title Fox News used, “Daily dose of diet soda tied to triple risk of deadly stroke.”

Rachel Johnson, professor of nutrition at the University of Vermont, said in an AHA release, “We need to be cautious in the interpretation of these results. It doesn’t prove cause and effect.”

In a blog post, Aaron Carroll, a professor of pediatrics and associate dean for research mentoring at Indiana University School of Medicine, argued the study had several important weaknesses, such as not accounting for:

  • Race or ethnicity;
  • Drug misuse;
  • Employment status; and
  • Family history of disease.

He also said because of how the study tracked disease incidence, some of the findings might be the result of chance. He concluded there is no “evidence that changing your behavior with respect to drinking diet soda will change any of these outcomes at all.”

The American Beverage Association in a statement pushed back against the study. “While we respect the mission of these organizations to help prevent conditions like stroke and dementia, the authors of this study acknowledge that their conclusions do not—and cannot—prove cause and effect,” the group said. It added, “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” (Barbash, “Morning Mix,” Washington Post, 4/21; AHA release, 4/20; Pase et al., Stroke, 4/20; Rossman, USA Today, 4/21; Carroll, The Incidental Economist, 4/21).

Post by Barb Flynn

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