Research has proved diet sodas to cause stroke and dementia
Excessive intake of sugar has been linked to a huge variety of health problems, many of them a consequence of the obesity that’s also linked to excessive sugar. That’s led many people to switch to drinks with artificial sweeteners that aren’t metabolized by the body. A new study is now suggesting that these sweeteners are associated with their own health risks, namely stroke and dementia. But the study doesn’t get into causality, and there’s enough oddities in the data to suggest that it’s not time to purge your fridge just yet.
The study, run by a collaboration of Boston-based researchers, relied on a cohort of individuals that had been recruited starting in 1971. On average, every four years since, the participants have completed follow-up surveys and had their health checked out. Over 5,000 people are in this cohort, and they provide a rich source of epidemiological data.
The authors started out intending to look at whether sugar-rich drinks increased the risk of strokes and dementia. So they eliminated a lot of people from this cohort because they’d previously experienced these or related issues. That reduced the study population considerably: under 3,000 for stroke, and under 1,500 for dementia.
Splitting the study
The authors divided these populations based on how many sugar-filled and diet drinks the participants reported having in a week. The boundaries between these groups were set arbitrarily in order to keep the number of people in each group similar. Thus, members of the group that consumed the most sugar averaged more than two sugar-filled beverages per day, which includes soft drinks and juice. The next group consumed upwards of three soft drinks a week, while the group that drank diet drinks were somewhere in between, at more than one a day.
While this won’t matter in terms of estimating risk for each of these factors, readers should note that the study measured very different doses.
The consumption of sugary and diet drinks was also measured two different ways. One was based on recent intake according to the most recent follow-up survey. The second was cumulative and based on the responses across the three most recent surveys. In addition, the researchers split up the outcomes: all stroke and ischemic stroke, all dementia and Alzheimer’s.
To complicate matters further, the authors analyzed their participants in three different ways. One way took into account only basic demographic information, like age and education. A second added lifestyle factors, like diet quality and physical activity. The third added basic medical statistics like blood pressure, heart problems, cholesterol levels, and more. A number of the things in this last model are known risk factors for stroke and dementia, so this would seem to be the most relevant analysis.
With all that, the researchers had something on the order of 108 individual statistical tests. At this point, a number of false positive results become inevitable. To have confidence in the results, you’d want to see some consistency across groups and things like dose effects.
And here, the results were mixed. There was remarkable consistency when it came to sugary drinks: absolutely none of the tests showed a statistically significant association with either dementia or stroke. So, the authors’ original hypothesis turned out to be a bust.
But things were different with diet drinks. Recent intake of diet sodas was associated with strokes, although there was no dose effect, and cumulative intake dropped below statistical significance. For ischemic strokes, the association was consistent across all groups, but again, there was no strong dose or duration effect. Interpreting these results is difficult, though they’re certainly worth looking into more carefully.
On the dementia side, things were a bit simpler. While some associations were statistically significant among the heavier drinkers, they vanished entirely when all the health indicators were taken into account. This was also true when cumulative consumption was analyzed. This suggests that both diet drink intake and dementia are probably both associated with one of the health issues controlled for in this statistical model.
What’s this tell us?
The authors’ conclusion is stark: “Artificially sweetened soft drink consumption was associated with a higher risk of stroke and dementia.” But that seems to be overselling the results for dementia. For stroke, there do seem to be more consistent associations that are worth following up on.
But, as the authors spend extensive time in the paper discussing, there’s no way of telling why this association exists at this point. “Sicker individuals [may] consume diet beverages as a means of negating a further deterioration in health,” they posit. “Indeed, in our study, diabetes mellitus—a known risk factor for dementia—was more prevalent in those who regularly consumed artificially sweetened soft drinks.”