Does your blood level of vitamin D affect your risk of a severe case of COVID-19? If so, what should you do? And if raising vitamin D levels reduces the risk of COVID-19, why haven't public health policymakers talked more about it?



I can answer the first two questions, but to answer the third question, you'll need to understand that those policymakers are motivated by something other than public health.



The Public Library of Science (PLoS) just published another study, reinforcing the importance of vitamin D in relation to COVID-19.



The authors concluded, “Among hospitalized COVID-19 patients, pre-infection deficiency of vitamin D was associated with increased disease severity and mortality.”



Does this mean that low vitamin D levels cause severe COVID-19 infections? No. Does the study show that raising vitamin D levels protects you from COVID-19? Not necessarily, but based on other research, such an assumption would be a pretty safe bet.



The majority of people on the planet have vitamin D levels well-below optimal, but those with deficient levels of vitamin D are at a much greater risk of numerous health problems. The table below shows some of them.



Health Problems Associated with Low Vitamin D LevelsFlu and respiratory infectionsInsulin resistance and diabetesHeart diseaseOsteoporosis and bone fracturesLower IQs of babiesAtopic dermatitisCancerDecreased adrenal hormonesDecreased strengthIncreased body fatLow birth weight of newbornsMultiple sclerosisPsoriasisRheumatoid arthritisSchizophreniaType I diabetes



As it relates to infections, low vitamin D levels have been consistently associated with higher risks of flu and respiratory infections. Again, we’re talking about association, not causation.



However, raising vitamin D levels through supplementation reduces the risk of the flu and respiratory infections, as well. Clinical research shows that vitamin D supplementation supports immune function.



I wrote the following in a previous blog post:




In one study, supplementing with 2000 IU of cholecalciferol has been shown to lessen the occurrence of cold and flu symptoms.



In another study published in 2010, children in Japan took 1200 IU of cholecalciferol or a placebo from December 2008 through March 2009. At the end of the study, 18.6% of the placebo group and 10.8% of the vitamin D group got the flu.



That’s a 42% reduction, using an amount that still isn’t enough to reach optimal levels in most people.



Interestingly, the CDC found that flu shot was only effective in 23% of people who got it based on 2014 data.
Vitamin D: Deficiency Symptoms And Benefits Of Supplementation



Vitamin D and COVID-19



Multiple studies now show that low vitamin D levels are associated with more severe COVID-19 infections. To remain objective, though, you have to keep in mind that low-vitamin D levels are associated with other factors that are associated with a greater risk of COVID-19 infections.



Aging, obesity, poor nutrition, and a lack of outdoor activity raise the risk of COVID-19 infection by themselves, while also increasing the likelihood that an individual is deficient in vitamin D.



A study published in JAMA in September of 2020 (yes, a year and a half ago) showed that low vitamin D levels were associated with a 77% increased risk of a COVID-19 infection.



Prior to that, a July 2020 study of 14,000 people showed “low plasma 25(OH)D levels appear to be an independent risk factor for COVID-19 infection and hospitalization.”



A November 2020 study determined the following:




Vitamin D level is markedly low in severe COVID-19 patients. Inflammatory response is high in vitamin D deficient COVID-19 patients. This all translates into increased mortality in vitamin D deficient COVID-19 patients. As per the flexible approach in the current COVID-19 pandemic authors recommend mass administration of vitamin D supplements to population at risk for COVID-19.
Jain A, et al.