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Does diet soda increase the risk of dementia and stroke?

Studies published in respected journals seem to indicate that diet soda increases the risk of stroke and dementia. Not to give a free pass to sugary drinks, one of the studies seemed to indicate that either artificially sweetened or sugar-filled drinks might be linked to a higher risk of Alzheimer’s disease, a form of dementia.

Of course, I’m sure you’ve seen headlines that say, “Diet Soda causes dementia,” without any critical analysis of the studies that might have claimed that.

As I usually do, I want to review this paper and see if it says what we think it says.

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Diet soda and dementia paper

In a study published in May 2017 in the journal Stroke, Matthew P Pase, Ph.D., Department of Neurology, Boston University School of Medicine, Boston, MA, and colleagues studied 2888 participants, age greater than 45 years (mean age was 62), for the occurrence of stroke. They also studied 1484 participants, aged greater than 60 years (mean age of 69), for the occurrence of dementia. Beverage intake was quantified using a questionnaire for each cohort.

The researchers adjusted the results for age, sex, education, caloric intake, diet quality, physician activity, and smoking, so most confounding variables were eliminated from the study. For example, the data was adjusted so that smokers, who might be more at risk for stroke, would not make up more of one group or another.

Below are the key results:

  • Individuals who had a higher recent and cumulative intake of artificially-sweetened soft drinks had a 2.96X higher risk for stroke.
  • That same group had a 2.89X higher risk for Alzheimer’s disease.
  • There was no change in the risk of stroke or dementia for those who consumed sugar-sweetened soft drinks.

However, the same research group, in an article published on 6 March 2017 in Alzheimer’s & Dementia, concluded that “higher intake of sugary beverages was associated cross-sectionally with markers of preclinical AD (Alzheimer’s disease).” So if you actually accept the findings of this paper, don’t count on drinking sugary drinks as being nutritionally superior to diet drinks.

Diet soda and dementia – my critique

I have several issues with this study that make me skeptical of the claims, which I list below:

  1. There is a lack of a plausible biochemical or physiological pathway whereby diet sodas would be causal to these two neurological issues.
  2. Confounding data could bias the results. For example, those who consume artificially-sweetened drinks could be more obese, smoke more, or exercise less, all of which are also linked to dementia and cardiovascular diseases such as stroke.
  3. The errors around the mean of most of the results were quite huge, and it included unity – in other words, there was a possibility that the results showed no increased risk to the consumption of these artificially sweetened drinks.
  4. The actual number of participants in this study who had either dementia or stroke was tiny – there were less than 100 individuals who had an ischemic stroke, while there were less than 60 individuals who had Alzheimer’s disease. Although one can show statistical significance with such low numbers, I’m always wary of unintentional bias showing up in such small numbers.
  5. The use of surveys has been questioned as to their utility and quality. Surveys depend on the accuracy of the participant, and they can be biased to provide information that they think the researchers want.
  6. This study can only show a correlation between the consumption of diet sodas and dementia or stroke, but it cannot show causation.
  7. I could find no other published studies that showed a link between Alzheimer’s disease and dementia. A fairly large study did show a statistically significant link between stroke and diet sodas – however, the increased risk was so small as to be almost clinically insignificant. Otherwise, there is little robust data out there that supports the hypothesis presented by Pase et al.


As I wrote above, I am concerned that this study may make it appear that drinking your favorite diet soda is eventually going to cause you to develop strokes, Alzheimer’s disease, or dementia. But examining the data closely, I am unconvinced that they have shown a link. I’m particularly concerned about confounding data that makes this study almost unusable.

If a person drinks diet sodas to reduce the symptoms of type 2 diabetes or reduce weight, both of which are linked to an increased risk of stroke, Alzheimer’s disease, and dementia, it could lead to a reduction of risk of those same diseases.

I just have not seen convincing evidence that diet sodas are risk factors for these neurological diseases.


Michael Simpson

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