“Canned response” (Diet soda study)


This past month, my Facebook feed has seen a frenzy focused on fizzy drinks. The panicky parade of posts tied diet soda to dementia, stoke, Alzheimer’s, and wearing linen out of season.

The alarm centered on one study, which was read by Dr. Harriett Hall, but likely not perused by those who posted the terrified screeds. By reading it, Hall learned that there were 2,888 subjects who were followed for 10 years, and that 97 of them had a stroke, while 81 of them developed dementia, most of those displaying symptoms consistent with Alzheimer’s. The authors relied on a survey of test subjects to determine how much diet soda each person consumed. All this lead to headlines which warned that drinking one or more artificially-sweetened soft drink per day was associated with a tripling of strokes, dementia, and Alzheimer’s.

While worried posters presumed correlation meant causation, even the lead researcher cautioned against reaching that conclusion. That man, Matthew Pase, said, “It is not clear whether the diet sodas are causing stroke and dementia or whether unhealthy people gravitate more towards these drinks than healthier people.”

Addressing these and other shortcomings in Fortune, Sy Mukherjee observed that an accurate description would be, “Study determines minor observational link, but no direct cause-and-effect, between certain people who drink artificial sugar beverages, but it has a small sample size that doesn’t include minorities or account for a whole bunch of other critical factors.” But there’s little click-bait or alarmist value in that.

Meanwhile, physician Aaron Carroll highlighted several reasons why you should take this study with a grain of, in this case, sugar. Carroll pointed out that while the conclusions were based on results from one model that adjusted for demographics, diet, physical activity, and smoking, another model which adjusted for still more potentially mitigating factors produced less-pronounced results. Yet this model received scant attention.  

Other deficiencies of the study: Various artificial sweeteners have different molecular makeups, meaning they likely have different impacts on the body; the study focused only on diet soda consumption and did not take into account the subjects ingesting artificial sweeteners through other food and drink; it highlighted relative risk rather than absolute risk, as it declared that subjects were thrice as likely to have stroke or dementia, instead of pointing out that the percentage of all subjects who had these conditions was one half of one percent. That would fit into what would be expected of the general population.

This response to this study was the latest in a long string of doom and gloom pronouncements about several artificial sweeteners that has been going on since at least the mid-1970s. Then, the worry was over saccharin causing bladder cancer in rats. While this was true if the rats were force fed large doses of saccharin, the cancer developed through a mechanism that humans lack. So the danger was for rodents and that’s only if they got into your Diet Dr Pepper and finished off a case in short order. Had there been any truth to the rumor, bladder cancer rates would have plummeted once other sweeteners supplanted saccharin.

In the war on cola, aspartame has been especially slandered. Critics have accused it of causing seizures, Alzheimer’s, arthritis, cancer, diabetes, multiple sclerosis, birth defects, tinnitus, migraines, emphysema, and (fill in the blank with your own malady). Yet, as Hall noted, aspartame is the most frequently evaluated food additive and the metadata of published studies show it is safe for anyone without the genetic disorder phenylketonuria. But those studies don’t get the headlines and the headlines that do get published usually misrepresent what studies say about carbonated refreshment.

It’s not that there could never, under any circumstance, be any harm in diet soda consumption. We should always be open to new evidence gained through double blind studies and follow where the science leads. But there is certainly harm in spreading fear through anecdotes, flawed studies, and misinterpretation of good data.


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