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Health A to Z  —  6 minutes

Vitamin D and COVID-19

January 26th, 2021
Dr Nicolas Tétreault, Clinical Biochemist, Ph.D., CSPQ, FCACB
Dr Nicolas Tétreault, Clinical Biochemist, Ph.D., CSPQ, FCACB
Scientific and Innovation Director

A Spanish study published in October 2020 in The Journal of Clinical Endocrinology & Metabolism found that 80% of patients with COVID-19 had a vitamin D deficiency compared to 40% of subjects in the control group who didn’t have COVID. [1] Another study also from Spain, a country heavily affected by the pandemic, showed that adding vitamin D to the usual inpatient treatment reduced admissions to intensive care. In this study, only one patient in 50 (2%) who received vitamin D supplements ended up in intensive care, compared to 13 in 26 patients (50%) who received basic treatment without vitamin D. [2]

Based on these results, it may be easy to conclude that vitamin D plays a role in preventing COVID-19. However, we need to ask the right questions: Do people infected with COVID-19 end up in hospital because they have a vitamin D deficiency or because they’re elderly, overweight or diabetic, which can lead to a vitamin D deficiency? It’s all in the details!

What’s so special about vitamin D?

The benefits of vitamin D on bone health have been known for decades. Over time, and as techniques for measuring vitamin D blood levels have improved, hundreds of publications have attributed protective effects to vitamin D against several illnesses, including various types of cancer, [3] multiple sclerosis, [4] Alzheimer’s disease [5] and diabetes. [6]

Nature of vitamins

Vitamins are essential chemical components that the human body is unable to produce either at all or in sufficient quantities, as is sometimes the case with vitamin D. Therefore, these essential elements must be obtained through our diet or supplements.

Our main source of vitamin D (vitamin D3) comes from the skin, which manufactures it from blood cholesterol. Another part comes from our diet in the form of vitamin D3 (meat and fish, supplements) and vitamin D2 (plants, supplements).

Vitamin D is then stored in the liver in an inactive form (Vitamin D 25-OH). To be activated, vitamin D must undergo a second transformation by the kidney cells (1,25 hydroxy Vitamin D). For this reason, people with severe kidney failure are unable to produce active vitamin D, even when taking large amounts of vitamin D2 or D3 supplements.

Roles of vitamin D

The best known role of vitamin D is to regulate calcium levels, which contributes to bone health. Vitamin D is essential not only for the absorption of dietary calcium by the gut, but also to prevent its elimination through the urine. In addition, vitamin D acts inside the bone to promote mineralization.

Besides this fundamental role, it can influence the expression of approximately 200 genes [7] in a wide variety of tissues. It’s this influence that may explain the many effects of a vitamin D deficiency. It’s also the reason for the more recent interest in maintaining vitamin D levels required to meet bone needs while providing other potential benefits.

Vitamin D deficiency versus insufficiency

It’s estimated that, depending on the season and latitude, exposure to the sun can provide 80%-90% of the required vitamin D. In the Northern Hemisphere, however, exposure to the sun is only maintained year-round south of the 35th parallel (a line that passes through northern Georgia and Alabama, then southern Nevada).

Because Quebec is located north of the 45th parallel, there’s not enough sunlight in the winter to allow the skin to produce sufficient amounts of vitamin D.

This means we have to rely on reserves accumulated in the liver during the summer months, on food intake and, if necessary, on supplements. This data must obviously be put in perspective with other factors, including age, skin type and pigmentation, clothing habits, time spent outdoors, etc.

Read more: The consequences of a vitamin D deficiency are critical for bone health.

Vitamin D deficiency

Vitamin D deficiency is any blood value below the reference values of the laboratory that performed the test. These reference values are obtained by measuring vitamin D blood levels in a “normal” population (i.e., people with no apparent signs of disease). The standard treatment for vitamin D deficiency is to take supplements in order to avoid deterioration in bone health. Groups at risk include people with kidney failure or osteoporosis as well as children who are breastfed.

Vitamin D insufficiency

Since reference values are based on subjects who are often young and without apparent signs of disease, it’s possible that some vitamin D levels, even if they fall within reference values, aren’t sufficient to provide long-term protection against cancer, Alzheimer’s disease or other illnesses. Several authors and learned societies have proposed raising the optimal or desirable level to more than 75 nanomol/liter of blood (nmol/L). [8]

According to Statistics Canada, only about a third of the Canadian population reached an optimal or desirable level of vitamin D from 2007-2009. [9]

However, because the non-bone effects of vitamin D are difficult to measure, there’s no consensus on the “desirable value” and, more importantly, how to maintain it. Vitamin D is a fat-soluble vitamin and, unlike water-soluble vitamins such as vitamin C or the group B vitamins, too much of it can accumulate (blood levels above 250 nmol/L) and lead to adverse effects such as headaches, nausea, vomiting and intense fatigue. If taken regularly over the long term, vitamin D supplements can also promote the formation of kidney stones.

Miracle vitamin?

While there’s no doubt that the effects of vitamin D go beyond good bone health, it’s difficult to separate them from other health aspects (e.g., diet, exercise, occupation, mental health, etc.). Therefore, it’s possible that acceptable vitamin D levels reflect the good habits of people who care about their health and try to prevent all kinds of diseases, including COVID-19. [10]

  1. Hernandez J. L. et al., “Vitamin D Status in Hospitalized Patients with SARS-CoV-2 Infection,” The Journal of Clinical Endocrinology & Metabolism (source consulted November 9, 2020)
  2. Castillo M. E. et al., “Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study,” The Journal of Steroid Biochemistry and Molecular Biology, vol. 203, October 2020, 105751
  3. Garland C. F. et al., “The role of vitamin D in cancer prevention,” Am J Public Health, 2006 February; 96(2): 252-261. doi: 10.2105/AJPH.2004.045260 (source consulted November 9, 2020)
  4. Ascherio A. et al., “Vitamin D and multiple sclerosis,” Lancet Neurol 2010; 9: 599-612
  5. Littlejohns T. et al., “Vitamin D and the risk of dementia and Alzheimer's disease,” Neurology, 2014; 83:1
  6. Mathieu C. et al., “Vitamin D and diabetes,” Diabetologia, vol. 48, p. 1247-1257 (2005)
  7. Ramagopalan S. V. et al., “A ChIP-seq defined genome-wide map of vitamin D receptor binding: associations with disease and evolution,” Genome Research,‎ 2010 (DOI 10.1101/gr.107920.110 (source consulted November 9, 2020)
  8. Gorham E. D. et al., “Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis,” Am J Prev Med, 2007 Mar;32(3):210-6. doi: 10.1016/j.amepre.2006.11.004 (source consulted November 10, 2020)
  9. Langlois K. et al., “Vitamin D status of Canadians as measured in the 2007 to 2009 Canadian Health Measures survey” (source consulted November 10, 2020)
  10. Perry Wilson, F., “Vitamin D for COVID? We’ve Been Burned Before” (source consulted November 8, 2020)