Reverse Causality in Health Research
In recent years, people have been taking charge of their own health. Going on research databases such as PubMed, WebofScience, and Scopus has become much more common. With the rise of social media, research studies are gaining massive attention from influencers and health gurus, who use them to help back their claims.
On the surface, this is a step in the right direction. In theory, this shares more evidence-based information and gives the public access to read the studies that create these claims. However, it can also lead to science being used to fuel mis-interpreted research. With many people not reading the studies that back these claims, and just digesting them at face-value, it leaves this gap for misinterpretation. This isn’t new and has been seen historically in news articles, newspapers, or if you really trace it back, your local pamphleteer (your news reporter of the late 1700s). But this is becoming more prominent now that more people are having a voice in the online space.
So, I wanted to write this blog to hopefully broaden your perspective on the concepts that you might see in studies you see propagated online.
What is Reverse Causality in Health Research?
Reverse causality in health research happens when it seems like one thing causes another, but the relationship could be the other way around.
This is common in research without a time-related aspect, like following participants over time. Without knowing in which order two things occurred, it is impossible to determine which caused the other.
For example, a study might find that people with depression exercise less. It might seem like not exercising causes depression, but it could be that having depression makes it harder for those people to exercise.
Less exercise can amplify symptoms of depression.
or
Depression makes it more challenging to exercise.
Without the temporal or time-related aspect to this example study, both of the above headlines could be concluded based on the data that less exercise and depression are related.
Reverse Causality and Artificial Sweeteners
The most famous examples of reverse causality involve artificial sweeteners. When a new study comes out, you bet your favorite health guru will be snatching up an item in the grocery store that’s artificially sweetened saying it will cause you to gain weight, ruin your hormones, or cause cancer.
Here are just some example studies that have observed a relationship between artificial sweeteners and weight gain, cancer, or cardiovascular disease risk.
I have seen all of these cited online by influencers; and they all label reverse causality as a limiting factor.
This means that it’s impossible to know for sure (from these studies at least), if the participants were gaining weight, or had a higher risk or incidence of disease because of the artificial sweeteners. They could be consuming more artificial sweeteners to combat the weight gain or disease risk.
What Does This Mean for Me?
Of course, this doesn’t prove anything. I am not here to tell you that artificial sweeteners are 100% safe, or exercise can’t aid in the treatment of clinical depression. I too am always seeking answers to help avoid things that could cause long-term impacts on my health.
I do hope however, that with this new information, you can read some of the research you have seen or do see cited by creators online and critically analyze them with a better understanding of this common limitation in health research.
