In high school, my AP Chemistry teacher was renowned for his daily consumption of Diet Dr. Pepper. There were bottles hidden in every nook and cranny of our classroom, and it was rumored that he hadn’t sipped a glass of water in years. As students we would whisper to each other in hushed tones, “That can’t be healthy, right?” Well, according to the headlines this week (I’m looking at you – Fox, USA Today, Washington Post and CNN), those beloved bottles of Diet Dr. Pepper just might increase one’s risk for dementia and stroke.
But hold your horses – before we make any drastic life changes, let’s unpack exactly what these headlines were all about.
A few days ago, a paper titled “Sugar and Artificially Sweetened Beverages and the Risks of Incident Stroke and Dementia” was published in Stroke Journal. The paper was written based on a prospective cohort study, or a study where a group of people were observed over a long period of time.
Based on data gathered from the observational studies, researchers found that individuals with a daily diet soda habit had approximately three times the risk of coming down with a stroke or developing dementia later down the road.
Tripling the risk sounds quite alarming, but the study authors don’t show what the actual risk for the non-diet soda swigging control group was – and this can make a huge difference. It could mean that 15% of diet soda guzzlers developed stroke or dementia compared to 5% in the control group – OR it could mean 0.03% as compared to 0.01%. Yes, the latter still represents a 3x risk; however, it’s a lot less scary than the former.
This numbers quibble aside, the study was purely observational, and for this reason alone, news outlets should have been more conservative in the way they covered the study. While observational studies can give us correlations, they cannot confirm the actual causes of the observed phenomena – and this should always be kept in mind when reading papers (or about papers) like this one.
In fact, the authors themselves warned about the observational nature of the study:
The observational nature of our study precludes us from inferring causal links between artificially sweetened beverage consumption and the risks of stroke and dementia.
If that’s not clear, I don’t know what is.
Next, the authors admit to a few other weaknesses in the methodology. For one, the particular group of people they studied did not include many minorities. Because of this, the findings might not be generalizable to other populations.
Another issue is that the relationship between artificial sweetener and dementia/stroke risk decreased when the researchers made adjustments for subjects with diabetes and hypertension. Diabetes on its own is a risk factor for stroke, and it is likely that diabetic soda-drinkers are more likely to opt for artificial sweeteners than their non-diabetic counterparts.
This is a classic example of a potential confounding variable – something going on behind the scenes that might affect the end result in ways that researchers don’t always account for. It is yet another reason why observational studies can be tricky to interpret.
Finally, while the researchers controlled for factors of age, sex, education, caloric intake, diet, physical activity and smoking history, they didn’t control for heart disease, race (because the data set had diversity issues), family history, obesity, and drug use. It should be noted that each one of those is also a risk factor for stroke (and there is a whole other list of risk factors for dementia).
It should be noted that the point of this post is not to discredit the study in any way. The researchers worked with the data they had, and found some interesting associations. However, as we’ve learned, these should be taken with a grain of salt.
Rather, the point of this post is to serve as a cautionary guide for to think about the click-bait style articles that are so often passed off as science.
The scientific method is rigorous, and researchers often work hard to publish their work in order to communicate with other scientists. Where this often goes wrong is when reporters who are not science literate pick up the study, skim the abstract, and write an alarmist headline that then goes viral on social media.
So should you give up your diet sodas and artificial sweeteners? Honestly, you can read the paper and decide for yourself.
What would my AP Chem teacher say? Well, he once told me that he could give up his Diet Dr. Pepper and eat healthy today, and still get hit by a bus tomorrow. So I know at least one person who won’t be giving up his sugar-free beverage.