Updated February 2022 / Originally posted March 2021

In a study published in the journal PLOS ONE, medical researchers from Israel show a correlation between vitamin D deficiency and respiratory infection severity. Patients with vitamin D deficiency were 14 times more likely to have severe or critical illness compared to those with blood levels of 25(OH)D3 that were above 40 ng/ml.

Why Over 200 Scientists And Doctors Call For Increased Vitamin D For All

In an open letter to public health officials, doctors, and healthcare workers, leading medical experts from around the world came together to make a strong statement regarding vitamin D’s health benefits to immune function.1

This letter falls on the heels of a similar case made in an Op-Ed in Medpage Today, on January 5, 2021, by former U.S. Surgeon General, Dr. Richard H. Carmona, who urged physicians to take responsibility and not to “wait for perfect evidence when making life-and-death decisions.2 

The consensus among researchers and physicians educated on the benefits and safety of vitamin D3 supplementation is clear – achieving adequate vitamin D status should be one of our highest public health priorities.1,2,4

What Does The Research Say About Vitamin D And Immune Function?

Vitamin D3 has health benefits beyond the bones and teeth. In particular, it is critical to immune function, especially in helping to protect against respiratory viral infection. There is scientific evidence that higher blood levels of vitamin D3, as well as vitamin D3 supplementation, are associated with a reduced rate of developing respiratory tract infections due to viruses.5-7

In a detailed review in one of the most well-respected sources in the world, the British Medical Journal, researchers assessed the results from 25 randomized controlled trials with a total of 11,321 participants, ranging in age from infancy to their mid-90s. Results showed that vitamin D supplementation produced a 70% decrease in respiratory tract infections in those with initial low vitamin D levels. In those without vitamin D deficiency, there was still a 25% reduction in respiratory tract infections.6

Who Are Most At-Risk For Vitamin D Deficiency?

Vitamin D deficiency may be the most common health challenge in the world as the vitamin is not readily available from food, but it can be formed when sunlight hits the skin to change a compound (7-dehydrocholesterol) in the exposed area of skin into vitamin D3.

Vitamin D deficiency is common because most of us spend most days indoors, or are covered up with clothes or sunscreen when outside. Residing at a high latitude (less sun exposure); aging (older skin is less responsive to sunlight); darker skin (melanin reduces the effects of ultraviolet rays on the skin); and obesity, liver disorders, and type 2 diabetes  – these conditions reduce the conversion of D3 to the more active 25-OH-D3 by the liver.

Vitamin D3 deficiency is diagnosed by having a blood level of 25-OH-D3 of less than < 20ng/ml. But adequate vitamin D levels are those above 30ng/ml, and optimal levels are thought to be in the range of 50 to 80 ng/ml.

Table 1 - Troubling Statistics on Vitamin D3 Deficiency in the United States

70% of the population have inadequate levels of vitamin D (blood levels below 30 ng/ml)

50% of the population is vitamin D deficient (blood levels below 25 ng/ml)

60% of all hospital patients are vitamin D deficient

76% of pregnant mothers are severely vitamin D deficient

80% of nursing home patients have inadequate vitamin D levels


Individuals with low vitamin D3  should be supplementing with vitamin D3 right now, there is just too much at stake not to. The 200 experts urging for widespread supplementation recommended the following:

  • Testing for blood levels of 25-OH-D3 to best determine status and dosage range for supplementation.
  • Adults currently not taking vitamin D3 or those with blood levels of 25-OH-D3 less than 30 ng/ml, should take 10,000 IU (250mcg) daily for 2-3 weeks.
  • After this loading dosage, adults should supplement at a dosage of 4000 IU (100mcg) daily. This dosage is universally regarded as safe.9
  • Adults at increased risk of deficiency due to excess weight, dark skin, or living in nursing homes may need a higher daily intake of 8,000 IU. Testing is best to determine dosage.


  1. https://vitamindforall.org/letter.html
  2. https://www.medpagetoday.com/infectiousdisease/covid19/90530
  3. https://vitamindforall.org/Carmona_letter_preamble.pdf
  4. Parva NR, Tadepalli S, Singh P, et al. Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012). Cureus. 2018 Jun 5;10(6):e2741.
  5. Pham H, Rahman A, Majidi A, Waterhouse M, Neale RE. Acute Respiratory Tract Infection and 25-Hydroxyvitamin D Concentration: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2019;16(17):3020. Published 2019 Aug 21. doi:10.3390/ijerph16173020
  6. Martineau Adrian R, Jolliffe David A, Hooper Richard L, Greenberg Lauren, Aloia John F, Bergman Peter et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data BMJ 2017; 356 :i6583
  7. Ginde AA, Blatchford P, Breese K, et al. High-Dose Monthly Vitamin D for Prevention of Acute Respiratory Infection in Older Long-Term Care Residents: A Randomized Clinical Trial. J Am Geriatr Soc. 2017;65(3):496-503. doi:10.1111/jgs.14679
  8. https://emerginnova.com/patterns-of-covid19-mortality-and-vitamin-d-an-indonesian-study/
  9. De Smet D, De Smet K, Herroelen P, Gryspeerdt S, Martens GA. Serum 25(OH)D Level on Hospital Admission Associated With COVID-19 Stage and Mortality. Am J Clin Pathol. 2021 Feb 11;155(3):381-388.
  10. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0263069
  11. https://www.medrxiv.org/content/10.1101/2021.06.04.21258358v1