Could Vitamin D Decrease Your Risk Of COVID-19? Here's What We Know

If there's one thing the entire world can agree on right now, it's that COVID-19 is top of mind. As the pandemic continues to be a reality, many people are taking extra measures to stay healthy and support immune strength—that includes getting more sleep, eating nutrient-rich foods, and breaking a sweat with plenty of at-home exercise.

Recently, a number of scientists and doctors have been discussing another measure to support immune and respiratory health: vitamin D.

The nutrient is associated with keeping a number of your body's systems running smoothly, including musculoskeletal, gastrointestinal, endocrine, and cardiovascular. And now, some experts even believe supplementing with vitamin D might help reduce the risk of COVID-191.*

It's important to acknowledge that at this time, however, there's no confirmed cure or guaranteed way to avoid contracting COVID-19. As far as preventive measures2 go, the Centers for Disease Control and Prevention (CDC) officially recommends washing your hands with soap and water frequently, socially distancing yourself from other people, covering your nose and mouth with a face mask in public, shielding your mouth and nose when you cough or sneeze, and disinfecting frequently used surfaces regularly. 

Vitamin D, which is classified as both a fat-soluble vitamin and a hormone, plays an important role in immune function3, according to a fact sheet published by the National Institutes of Health (NIH).

While scientists' understanding of the interaction between vitamin D and the immune system4 has developed significantly over the last 20 to 30 years, there are still a number of questions researchers are working to understand. That said, "There’s no disagreement between scientists and doctors that vitamin D is important for the immune system," Harvard geneticist David Sinclair, Ph.D., told mbg in a recent interview. "Our immune cells need vitamin D to function."

Vitamin D is thought to play a crucial role in promoting immune response5 by enhancing the production of antimicrobial agents, according to a research review published in the Central European Journal of Immunology.* What's more, findings from a recent in vitro study imply vitamin D activates certain genes6 involved in the immune response.*

"Immune cells are favorably affected by vitamin D levels," Heather Moday, M.D., previously told mbg.* And on the other end of the spectrum, "vitamin D deficiency is associated7 with increased frequency of infection."* There is also mounting evidence linking vitamin D deficiency7 and autoimmune diseases, such as rheumatoid arthritis and irritable bowel syndrome, according to a research review published in the Journal of Investigative Medicine.

Vitamin D deficiencies are more common than you may think: One study estimates that 1 billion8 children and adults worldwide are deficient. While there's not a defined optimal range for vitamin D, "people who have about 40 ng/mL to 60 ng/mL in their blood tend to have the lowest mortality but also do better when they get viral infections," says Sinclair.

Many experts have also drawn associations between vitamin D and lung health.* Namely, researcher Rhonda Patrick, Ph.D., was one of the first scientists to speak openly about the potential of vitamin D protecting against lung injury.*

One meta-analysis published in BMJ, for example, specifically looked at the overall effect of vitamin D supplementation on respiratory tract infections9. Researchers reviewed data from 10,933 participants and found vitamin D supplementation was safe and reduced the risk of acute respiratory tract infection among all subjects.* The researchers also noted that patients who were very vitamin D deficient experienced the most benefit.*

A different research review stated that vitamin D deficiency is very common among patients with respiratory diseases10, and there may be a connection between the two. However, further research is needed before drawing any conclusions. 

The most common way to get vitamin D is by spending time outdoors in the sun. However, if you aren't able to absorb ample sunshine—whether that's because it's winter or you're sheltering-in-place—you may need to get vitamin D from other sources.

For example, there are a number of vitamin-D-rich foods that you can incorporate into your diet. Some of the best sources include fatty fish (such as salmon, tuna, and mackerel), fish liver oils, egg yolks, mushrooms, and fortified products, according to the NIH11. However, most foods don't have high enough levels of the hormone, says Hyman, which means you may need to supplement to reach adequate levels.*

The NIH recommends11 400 to 800 IUs of vitamin D a day, but that's mainly to prevent rickets, a disease caused by vitamin D deficiency, says Hyman.