Updated: If vitamin D affects the severity of Covid-19 cases, we should see relief from the pandemic from June through October, and the worst period would be from November 2020 to May 2021. See “L.” below.
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There is sufficient evidence from studies to recommend that every adult take 10,000 IU of vitamin D as a supplement, to strengthen the immune system and possibly to reduce risk of a severe case of Covid-19.

The evidence is compelling. A dose of 10,000 IU/day in adults is safe. And there are multiple studies plus expert commentary indicating that vitamin D may reduce risk of a severe case of Covid-19. Many adults, especially the elderly, have a vitamin D deficiency. And staying indoors most of the time makes that worse. If it turns out that vitamin D does not have the good effect protecting people, to a limited extent, from a severe Covid-19, it does certainly strengthen the immune system. And it is an essential nutrient. So you really cannot go wrong taking a vitamin D supplement. Start now. Do not wait until you are sick, as it takes weeks or months to slowly raise your blood levels of vitamin D.

Studies on Vitamin D versus Covid-19:

1. “Vitamin D supplementation could possibly improve clinical outcomes of patients infected with Covid-2019 based on increasing odds ratio of having a mild outcome when serum (OH)D level increases.”

Alipio, Mark. “Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-2019).” Available at SSRN 3571484 (2020). Link

The first study found that only 3.6% of persons with normal Vitamin D levels had severe or critical cases of #COVID19, whereas 79.2% of persons deficient in Vitamin D had severe or critical cases. Subsequent studies support this conclusion.

2. “Strikingly, 100% of ICU patients less than 75 years old”, who were diagnosed with Covid-19, had Vitamin D Insufficiency.

Lau, Frank H., et al. “Vitamin D insufficiency is prevalent in severe COVID-19.” medRxiv (2020). Link

3. “our finding suggests that Vit D may reduce COVID-19 severity by suppressing cytokine storm in COVID-19 patients.”

Daneshkhah, Ali, et al. “The Possible Role of Vitamin D in Suppressing Cytokine Storm and Associated Mortality in COVID-19 Patients.” medRxiv (2020). Link

4. “Recent and historical data are highly consistent with a causal protective role for Vitamin D in respiratory disease risk and especially in the case of COVID-19…. Vitamin D supplementation is an effective, safe and cheap method to protect against seasonal respiratory diseases and can play a key role in combatting the COVID-19 pandemic.”

Davies, Gareth, Attila R. Garami, and Joanna C. Byers. “Evidence Supports a Causal Model for Vitamin D in COVID-19 Outcomes.” medRxiv (2020). Link

5. “Vitamin D supplementation might be an inexpensive, accessible and safe mitigation for the SARS-CoV-2 pandemic.”

De Smet, Dieter, et al. “Vitamin D deficiency as risk factor for severe COVID-19: a convergence of two pandemics.” medRxiv (2020). Link

6. “KEY FINDINGS:
“Majority of the COVID-19 cases with insufficient and deficient Vitamin D status died.
“The odds of death was higher in older and male cases with pre-existing condition and below normal Vitamin D levels.
“When controlling for age, sex, and co-morbidity, Vitamin D status is strongly associated with COVID-19 mortality.”

Raharusun, Prabowo. “Patterns of COVID-19 Mortality and Vitamin D: An Indonesian Study.” Available at SSRN 3585561 (2020). Link

7. Ilie, Petre Cristian, Simina Stefanescu, and Lee Smith. “The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality.” Aging Clinical and Experimental Research (2020): 1. Link

8. Glinsky, Gennadi V. “Genomics-guided tracing of SARS-CoV-2 targets in human cells identifies Vitamin D and Quercetin as candidate medicinal agents for mitigation of the severity of pandemic COVID-19.” Link

9. In this study, persons with a positive test for Covid-19 had statistically significant lower blood Vitamin D levels as compared to persons who were negative for Covid-19; this association remained when patients were divided according to age.

D’Avolio, Antonio, et al. “25-Hydroxyvitamin D Concentrations Are Lower in Patients with Positive PCR for SARS-CoV-2.” Nutrients 12.5 (2020): 1359. Link

10. Nations with low vitamin D in the population have high infection rates and high death rates from Covid-19.

Laird, E., et al. “Vitamin D and Inflammation: Potential Implications for Severity of Covid-19.” Ir Med J; Vol 113; No. 5; P81: 2020. Link

11. Covid-19 patients with low vitamin D were at more than three times the risk of requiring intubation (for respiratory distress).

Faul, J.L., et al. “Vitamin D Deficiency and ARDS after SARS-CoV-2 Infection.” Ir Med J; Vol 113; No. 5; P84: 2020. Link

Articles or Non-Covid-19 Studies:

a. “To reduce the risk of infection, it is recommended that people at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d. The goal should be to raise 25(OH)D concentrations above 40–60 ng/mL (100–150 nmol/L). For treatment of people who become infected with COVID-19, higher vitamin D3 doses might be useful.”

Grant, William B., et al. “Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths.” Nutrients 12.4 (2020): 988. Link

b. Panarese, Alba, and Endrit Shahini. “Covid‐19, and vitamin D.” Alimentary Pharmacology & Therapeutics (2020). Link

c. This study answers the question, Can an entire nation raise the Vitamin D blood levels of its population? Yes. Finland did so.

Jääskeläinen, Tuija, et al. “The positive impact of general vitamin D food fortification policy on vitamin D status in a representative adult Finnish population: evidence from an 11-y follow-up based on standardized 25-hydroxyvitamin D data.” The American journal of clinical nutrition 105.6 (2017): 1512-1520. Link

d. Turashvili, Nino, and Lali Javashvili. “Could vitamin D reduce the risk of COVID-19?.” Translational and Clinical Medicine-Georgian Medical Journal 5.1 (2020): 4-6. Link

e. Jeyaraman, Madhan, Arun Gulati, and Talagavadi Channaiah Anudeep. “Vitamin-D an Immune Shield Against nCOVID-19.” Int J Cur Res Rev| Vol 12.09 (2020): 19. Link

f. Arboleda, John, and Silvio Urcuqui-Inchima. “Vitamin D supplementation: a potential approach for COVID-19 therapeutics?.” (2020). Link

g. Jakovac, Hrvoje. “COVID-19 and vitamin D—Is there a link and an opportunity for intervention?.” American Journal of Physiology-Endocrinology and Metabolism 318.5 (2020): E589-E589. Link

h. Rhodes, Jonathan M., et al. “low population mortality from COVID‐19 in countries south of latitude 35 degrees North–supports vitamin D as a factor determining severity.” Alimentary pharmacology & therapeutics (2020). Link

i. 10,000 IU/day needed to raise blood levels for adult population. Even 40,000 IU/day is not a toxic dosage.

Garland, Cedric F., et al. “Vitamin D supplement doses and serum 25-hydroxyvitamin D in the range associated with cancer prevention.” Anticancer research 31.2 (2011): 607-611. Link

j. Doses of 10,000 IU/day do not raise blood vitamin D above normal and safe levels. “Doses of ≤ 10 000 IU vitamin D/d (250 μg/d) for up to 5 mo do not elevate circulating 25-hydroxyvitamin D to concentrations > 90 ng/mL, whereas doses < 1000 IU/d appear, in many cases, to be inadequate…"

Doses of 400 IU/day are woefully inadequate: "What effect does a daily dose of 400 IU vitamin D for an extended time (months) have in adults? The answer is little or nothing. At this dose (10 μg/d) in an adult, circulating 25(OH)D concentrations usually remain unchanged or decline."

Article also refutes claim that high vitamin D intake causes disturbances in calcium metabolism. And it establishes that 10,000 IU/day of vitamin D is safe for pregnant and lactating women.

Hollis, Bruce W., and Carol L. Wagner. "Assessment of dietary vitamin D requirements during pregnancy and lactation." The American Journal of Clinical Nutrition 79.5 (2004): 717-726. Link

k. “Vitamin D deficiency is common and may contribute to increased risk of respiratory infection including Covid-19. We recommend that all older adults, hospital inpatients, nursing home residents and other vulnerable groups (e.g. those with diabetes mellitus or compromised immune function, those with darker skin, vegetarians and vegans, those who are overweight or obese, smokers and healthcare workers) be urgently supplemented with 20-50µg/d of vitamin D to enhance their resistance to Covid-19, and that this advice be quickly extended to the general adult population.”

McCartney, D. M., and D. G. Byrne. “Optimisation of Vitamin D Status for Enhanced Immuno-protection Against Covid-19.” Irish medical journal 113.4 (2020): 58. Link

l. Vitamin D levels in the United States are highest in the months around August, and lowest in the months around February (Kasahara, 2013). If vitamin D affects the severity of Covid-19 cases, we should see relief from the pandemic from June through October, and the worst period would be from November 2020 to May 2021.

Kasahara, Amy K., Ravinder J. Singh, and Andrew Noymer. “Vitamin D (25OHD) serum seasonality in the United States.” PloS one 8.6 (2013).
Link

Videos:
* Dr. Oz
* Dr. Seheult of MedCram
* Dr. Seheult’s daily regimen (Vitamins D, C, Quercetin, NAC)
* Dr. Mobeen of Drbeen Medical Lectures

How Much Vitamin D?

The above studies (a., i., and j.) suggest that 10,000 IU/day would be needed to obtain sufficient levels of Vitamin D, and would be safe for all adults.

I personally am taking 10,000 IU of Vitamin D3 per day.

RLCJ