Vitamin D is known to play a role in healthy immune system function.
If further research confirms that vitamin D may help prevent people from contracting COVID-19, it could become a relatively cheap and scalable strategy to stop the spread of the virus.
You can get vitamin D through sunlight, diet, supplements, and prescription.
Vitamin D deficiency is surprisingly common in the U.S., affecting about 42 percent of the population. Studies have linked low levels of vitamin D (which is actually a hormone, not a vitamin) to fatigue, muscle and bone pain, bone and hair loss, weakened immune system, dry skin, and depression.
Now, new research suggests that vitamin D deficiency may also increase the odds of contracting and suffering more severe complications from COVID-19.
One study, published September 25 in PLoS ONE, tracked the health of 235 patients in Iran who had contracted COVID-19. After controlling for confounding variables, the researchers found a significant association between vitamin D deficiency and more severe COVID-19 complications, including death.
The researchers wrote that patients who had healthy levels of vitamin D "had a lower risk of becoming unconscious and becoming hypoxic."
"Patients who were vitamin D sufficient had significantly lower blood levels of the inflammatory marker CRP and had a higher total blood lymphocyte count suggesting that vitamin D sufficiency had improved the immune function in these patients and raising the inflammatory markers," the researchers wrote. "This beneficial effect on the immune system may also reduce the risk of acquiring this insidious potentially life-threatening viral infection."
'Inexpensive, safe and scalable'
A second study, published in the October edition of The Journal of Steroid Biochemistry and Molecular Biology, found that hospitalized COVID-19 patients who were given a high dose of Calcifediol (a metabolite the body produces from vitamin D) experienced less severe complications than other patients who received similar care, but not Calcifediol.
Of the 50 patients who received Calcifediol, none died, but two of the 26 patients who didn't receive the metabolite did.
"Calcifediol seems to be able to reduce severity of the disease," the researchers wrote. "But larger trials with groups properly matched will be required to show a definitive answer."
The two studies were published in the wake of a retrospective study, published September 3 in JAMA, that analyzed 489 people who were tested for COVID-19 by UChicago Medicine. All of those people had also had their vitamin D levels tested within the past year. The study found that people with an untreated vitamin D deficiency were nearly twice as likely to test positive for COVID-19.
David Meltzer, Chief of Hospital Medicine at UChicago Medicine and lead author of the study, said that while the results don't establish causation, the relationship is worth studying further.
"Understanding whether treating vitamin D deficiency changes COVID-19 risk could be of great importance locally, nationally and globally," Meltzer told UChicago News. "Vitamin D is inexpensive, generally very safe to take, and can be widely scaled."
But despite the growing body of evidence linking vitamin D deficiency with more severe COVID-19 outcomes, it's important to note that scientists still don't fully understand how vitamin D interacts with COVID-19.
"There is biological plausibility for benefit of vitamin D, since it is known to regulate innate and adaptive immunity in ways that might reduce the viral load in patients exposed to SARS-CoV-2 and mitigate the severity and consequences of cytokine storm," Dr. Michael Lewiecki, of the University of New Mexico School of Medicine in Albuquerque, told Medscape.
"However, it is important to recognize that associations reported in observational studies do not necessarily mean there is a causal relationship. It may be that higher vitamin D is a marker of better health and lower baseline risk of complications of COVID-19."
Healthy levels of vitamin D
Although there's debate on the importance of vitamin D levels, it's probably a good idea to make sure you're not deficient in vitamin D. A healthy range is generally considered to be between 20 and 50 nanograms per milliliter of blood (though certain populations may require higher levels).
You can get more vitamin D by spending time in sunlight; eating fatty fish, egg yolks, mushrooms and fortified foods; taking supplements (note the differences between vitamin D2 and vitamin D3); or getting a doctor's prescription for a specific type of vitamin D.
But note that consuming too much vitamin D can be toxic, as the National Institutes of Health warns:
"The daily upper limit for vitamin D is 25 mcg to 38 mcg (1,000 to 1,500 IU) for infants; 63 mcg to 75 mcg (2,500 to 3,000 IU) for children 1-8 years; and 100 mcg (4,000 IU) for children 9 years and older, adults, and pregnant and lactating teens and women. Vitamin D toxicity almost always occurs from overuse of supplements."