If your vitamin D level is below 30 ng/mL, you are at increased risk for contracting COVID-19. A review of 40 studies showed that adequate vitamin D reduced the frequency and severity of COVID-19 infections and hospital admissions, and lowered the death rate (BMJ, Oct 5, 2020;371:m3872). Another review of 86 papers showed the benefits of vitamin D for all aspects of COVID-19 infections (Front Public Health, Sept 10, 2020;8:513). Several studies show that vitamin D deficiency has been associated with increased death rate from COVID-19 (Scientific Reports, Nov 19, 2020;10:20191; Eur J of Endo, medRxiv, May 7, 2020; JAMA Netw Open, Sept 3, 2020;3(9):e2019722).

The most recent studies suggest that you should take vitamin D pills to raise blood levels above 30 ng/mL, and most people can do this by taking 1000 IU pills each day. There is no evidence that higher doses of vitamin D offer greater protection from COVID-19 than moderate doses. Blood levels higher than 60ng/mL can cause serious tissue damage.

Vitamin D Strengthens Your Immune System
Vitamin D helps your immune system to fight off the effects of COVID-19. Doctors are treating severe COVID-19 with dexamethasone, which has a similar steroid structure to that of vitamin D. COVID-19 can kill by causing an overactive immune system called “cytokine storm, ” and vitamin D helps to reduce cytokine storm by decreasing the production of T helper cells and inflammatory cytokines (APMI, 2019;127:681-687), and by increasing anti-inflammatory cytokines (Nutrients, 2020;12:E236).

Vitamin D deficiency is associated with other risk factors for severe COVID-19, such as obesity, diabetes, older age or darker skin (NFS Journal, Aug 2020;20:10-21; BMJ Nutrition, Prevention & Health, May 13, 2020).

How Common is Vitamin D Deficiency?
About 42 percent of North Americans have low levels of vitamin D, including 82 percent of African-Americans and 70 percent of Hispanics (Nutr Res, Jan 2011;31(1):48-54). You need to get vitamin D from sunlight exposure, the foods that you eat, or vitamin D pills. Foods that contain some vitamin D include cold-water fish such as salmon, herring, sardines or mackerel, and red meat, liver and egg yolks. Many North Americans get enough vitamin D in the summer, but need pills or fortified foods in the winter months. In warmer weather, you can usually get enough vitamin D with 10 to 20 minutes of sunlight exposure of a small area of skin 3-5 times a week.

Do Not Overdose on Vitamin D
You cannot be poisoned by vitamin D through sun exposure or diet alone, but vitamin D poisoning can occur when people take high-dose supplements for an extended time. Unless your doctor prescribes higher doses, you should not take more than 2000 IU/day. Vitamin D is harmless in your body when it is bound to vitamin D receptors and carrier proteins. (J Clin Endocrinol Metab, 1986 Oct;63(4):954-9). However, having extra vitamin D floating in your system overwhelms vitamin D receptors to cause a marked increase in calcium to be absorbed from your gut (Am J Clin Nutr, 2004 Dec;80(6 Suppl):1689S-96S) and removed from your bones (Oman Med J, 2011 May;26(3):201-4) to cause high blood calcium levels that can bind to and damage every cell in your body.

High blood calcium levels from excess vitamin D can cause bone loss, brittle bones and bone pain. People who took high doses of vitamin D (4000 and 10,000 IU/day) for three years lost far more bone than those who took the recommended 400 IU/day (J Bone and Mineral Research, September 11, 2020). High levels of vitamin D also cause low levels of vitamin K2, with resultant loss of bone (Med Hypotheses, 2007;68(5):1026-34). Vitamin K2 helps to keep calcium in bones.

After several months of having high blood calcium levels and having no symptoms at all, you can develop kidney failure and not even know it. You may develop nausea, vomiting, diarrhea, constipation or muscle weakness. You can also develop high blood pressure, kidney stones, or calcium in your arteries to increase risk for a heart attack. Since vitamin D accumulates in and is released very slowly from fat, it can take months for blood levels of vitamin D to return to normal.

My Recommendations
I think that everyone should get a blood test for hydroxy vitamin D, particularly in the winter months when your levels are likely to be lowest. During this pandemic, you should not let blood levels of hydroxyvitamin D drop below 20 ng/mL and most recent papers now recommend 30 ng/mL or more. Unless your doctor recommends higher doses, you should not try to get levels much higher than 30 ng/mL, since very high levels can harm you.

If your blood levels of hydroxy vitamin D are below 30 ng/mL, take vitamin D3 pills of at least 1000 IU/day for one to two months. If your blood levels of vitamin D do not return to normal, check with your doctor about taking higher doses or getting a medical evaluation for the cause of your deficiency.

Anyone suspected of being infected with COVID-19 should get a hydroxy vitamin D blood test and immediately start taking vitamin D3 supplementation if the blood level is below 30 ng/mL.