New research published in the Irish Medical Journal purports to demonstrate a correlation between vitamin D levels and COVID-19 death rates. In other news, mothers around the world are taking the opportunity to gloat and say, "I told you so." They said from the start that we should eat our vegetables, but we didn't want to listen. Once again, science vindicates the moms.
The study was a collaboration between epidemiologists at Trinity College in Dublin and the University of Liverpool. The scientists find circumstantial evidence that vitamin D deficiency exacerbates the risk of coronavirus contraction and fatality and vice versa.
The researchers analyzed longitudinal data from as long ago as 1999, tracking vitamin D levels by population, grouping different communities according to geographical latitude. People living in Southern European countries, such as Spain and Italy, tended to be more vitamin-D deficient, whereas northerners, in places including the Nordic countries, generally had a sufficient amount.
This correlation comes as a surprise, considering that vitamin D typically enters the body through sunlight, not to mention though food or direct supplements. People living at low latitudes and, therefore, closer to the equator obviously get more exposure to sunlight.
The study then cross-applies these figures to records published by the World Health Organization (WHO). The WHO numbers show lower infection and fatality rates in the northern places, suggesting the possibility of a connection between vitamin D and immune system capability. People who possess the requisite amount of the nutrient, the hypothesis goes, have healthier, more robust bodies that put up more of a fight against invasive diseases.
It needs to be pointed out that this research does not establish a definitive connection. Correlation and causation, of course, do not necessarily overlap. While a cause definitely means some correlation, the presence of correlation could be superficial. In other words, vitamin D deficiency in places suffering worse consequences from the coronavirus might be a coincidence.
As previously mentioned, people receive vitamin D from food and supplements as well as sunlight. The healthier population of a somewhat dreary, sunlight-starved place such as Denmark suggests that the country has superior diet, healthcare, or both than its southern neighbors. If northern countries have desirable healthcare systems (and they typically do), then couldn't that factor alone account for the disparity in outcomes? Looking at the story from this angle, the vitamin D numbers look less like an authoritative cause and more like happenstance.
It seems that the epidemiologists may have begged the question slightly by searching for a statistical relationship between infection and nutritional value. Of course, they were going to find one because people who are nutrient-sufficient are healthier, by definition, and better able to combat viruses. This kind of circular reasoning is a common problem stretching back into the annals of popular science—pulp medicine one step removed from some sort of daytime TV quack saying that actually red wine and dark chocolate hold the keys to a longer life.
The Irish Medical Journal article didn't produce a single iota of original statistics. The researchers didn't conduct any experiments of their own. To be fair, however, they don't claim to have authoritatively established a link between vitamin D and coronavirus. They only call the disproportion in the numbers "statistically significant."
By their own admission, a more controlled study would be required in order to establish such a relationship. For example, if there were two people living at the same latitude with identical bank accounts, health insurance plans, etc., then those people's outcomes would be far more compelling. The vitamin D factor would be considerable.
While this evidence may leave much to be desired, there's no need to discount it out of hand. It isn't as if there's any danger to be found in increasing a person's vitamin D intake. Doctors have long believed that vitamin D has important implications for bone health and guarding against potential maladies such as osteoporosis.
Furthermore, vitamin D is accessible. Foods that most people eat, including eggs, dairy products, and seafood, are rich in it. Anyone could stand to get outside a little more, especially now. Supplements can be found at every drug store. As the researchers conclude, the story they're telling about nutrition and coronavirus is "plausible," at the very least. Heeding the scientists' warning is a win-win scenario.