Even by an incredibly low standard (30 ng/mL or 75nMol/L), 75% of teens and adults in America are woefully deficient in Vitamin D: https://www.scientificamerican.com/article/vitamin-d-deficiency-united-states/. Westerners aren’t healthy people, especially in the Northern Hemisphere this time of year. I’m always shocked when someone claims that an adult in America is “healthy.” We aren’t. We eat depleted food from depleted soil: https://www.scientificamerican.com/article/soil-depletion-and-nutrition-loss/ . We aren’t active: https://www.chicagotribune.com/lifestyles/health/ct-americans-inactive-computers-blame-20190423-story.html . We don’t get out in the sun; and, even when we do, we don’t have bodies which are healthy enough to synthesize all the necessary hormones which help us live, let alone thrive. No one is saying that Vit D is the cure; but our mismanaged health is certainly doing us no favors. And inadequate vitamin D is part of that equation.
The coronavirus exposes our unhealthiness in a way unlike few other contagions. Children are least affected. Aging populaces are most affected. Likewise, children have the rarest incidence of obesity, insulin resistance, and Vitamin D deficiency. Aging populations have the highest incidence. People with darker skin are more affected than people with lighter skin by coronavirus. Likewise, people with darker skin have higher propensity toward inadequate Vitamin D: https://academic.oup.com/jn/article/136/4/1126/4664238. Poorer communities are more affected than wealthier communities: https://time.com/5821212/coronavirus-low-income-communities/. Low income communities have lower Vitamin D levels: https://www.mayoclinicproceedings.org/article/S0025-6196(11)61465-1/fulltext. Whatever other string of associations you explore (latitude, cultural practice of vitamin supplementation, autoimmune compromised individuals, and EVERY health condition risk factor), Vitamin D crops up in the variables.
Even when we start to examine outlier cases, like “healthy” people who succumbed to coronavirus, their actual underlying health is questionable. Remember, 75% of Americans are below a low standard. What percent are below optimal? We don’t even know, because we set the bar so low. What we do know is that up to 80% of athletes, including elites, are at insufficient levels of a Vitamin D: https://www.ncbi.nlm.nih.gov/pubmed/20818195. Keep in mind that we use Vitamin D for many processes in the body. Thus, athletes deplete it at a faster rate than the general populace. And endurance athletes in long training sessions deplete it more than anyone. We shouldn’t be surprised at athletes getting sick. We should expect it.
These factors have led a variety of researchers to explore the association between Vitamin D status and Covid symptom severity: https://www.grassrootshealth.net/wp-content/uploads/2020/04/Grant-GRH-Covid-paper-2020.pdf. In preliminary findings and peer-reviewed results, there is a statistically significant correlation between Vitamin D status and severity of symptoms: https://www.grassrootshealth.net/blog/first-data-published-covid-19-severity-vitamin-d-levels/ (link for photo above). In an MDPI paper in Nutrients, authors made recommendations to take 10,000 ius of Vitamin D weeks ago: https://www.ncbi.nlm.nih.gov/pubmed/32252338. And the full-length paper describes the roles of other nutrients (including E) in the matrix of health and immune benefit: https://www.mdpi.com/2072-6643/12/4/1181/htm. TILDA, as well, noted that there are statistically significant connections between Vitamin D status and severity of respiratory infections: https://tilda.tcd.ie/publications/reports/pdf/Report_Covid19VitaminD.pdf.
Is this the smoking gun? No. Health is complex. Vitamin D levels must coexist among other nutrients and variables. What we call health has incredibly intricate features. Stress management, purpose, sleep, recovery, inflammation don’t have one single factor or contributor. But Vitamin D is assuredly part of the equation, and paying attention to it is a very simple step for most people to take. We aren’t likely to get religion to transform health overnight. Tomorrow we'll know more. Today, at the very least, we can seek adequate levels of necessary nutrients.