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Vitamin D: Role in COVID-19 Protection and Other Benefits

What is Vitamin D?

Vitamin D, also known as calciferol, is a naturally occurring vitamin in our body. It is a fat-soluble vitamin and exists in multiple forms. In food and dietary supplements, it naturally exists in 2 forms: Vitamin D2 (Ergocalciferol) and Vitamin D3 (Colecalciferol). Vitamin D is also produced within the body when it is exposed to UV rays. It will then undergo a two-stage activation in the body, first by the liver, then by the kidneys[1].

Deficiency in vitamin D can lead to several diseases, such as a loss of bone density (and eventually leading to osteoporosis and easily broken bones). In children, severe vitamin D deficiency can lead to a disease called rickets. In adults, this can lead to a condition called osteomalacia, where the bones become soft and may experience bone pain[2,3].

Other than its effect on the bones, there are also growing evidence with respect to vitamin D’s role in boosting a person’s immunity, which is especially important in this COVID-19 pandemic climate. Read on to find out more about the different functions of vitamin D.

Function #1 of Vitamin D: Immunity

In previous studies, vitamin D has been shown to be able to modulate the immunity responses in our body[4]. There are also reports and studies to show an association between low levels of vitamin D and higher incidences of upper respiratory tract infections (URTI)[5]. Also, there has been increasing evidence linking vitamin D deficiency with autoimmune diseases, such as rheumatoid arthritis (RA) and inflammatory bowel diseases (IBD)[6]. These effects could be thought to be due to the immune cells being able to respond to vitamin D in the presence of vitamin D receptors on them[4].

Vitamin D and COVID-19

COVID-19 pandemic has plagued the world for more than 2 years, starting from early 2020. There are more than 400 million people worldwide that has been infected with COVID-19, resulting in more than 6 million deaths[7]. There have been several suggestions on how vitamin D could be used as a supplement to help combat COVID-19 infection by boosting the immune system.

A sufficient level of vitamin D in the body is reported to be able to lessen the effects on increased inflammatory markers and cytokine storm in COVID-19 infection[8], and that vitamin D deficiency could be associated with a more severe COVID-19 infection, including mortality.

A study was conducted in 2021 September, where investigators collated and analyze 21 trials that looked at the association between vitamin D and COVID-19 infection[9]. The authors concluded that a low level of vitamin D may have the potential to increase the risk of COVID-19 infection and severe disease. They have also suggested to add vitamin D supplementation to COVID-19 prevention and treatment protocols.

Similar studies have also been carried out to study the association between vitamin D levels and COVID-19 infection. Chiodini I et al. also performed a systematic review of 54 studies and found that low levels of vitamin D were associated with ICU admissions, mortality, hospitalizations, and infection rate of COVID-19[10]. Dror A et al. also studied Israel registries of patients that had COVID-19 infections and found that lower levels of vitamin D were more common in patients with severe or critical disease[11].

Function #2 of Vitamin D: Bone health

Traditionally, Vitamin D has also been known to be beneficial for bone health. Vitamin D increases absorption of calcium and maintains normal levels of calcium and phosphate[1]. This helps keep the bones strong and avoid complications such as osteoporosis and osteomalacia. Research has shown that low levels of vitamin D intakes over a long period of time can lead to demineralization of the bones[12].

Vitamin D increases the absorption of calcium, and this feedback will decrease the breakdown of the bones by the body (to maintain sufficient calcium levels) [12]. Therefore, it is important to have sufficient intake of vitamin D to prevent and minimize risk of fractures, especially when you age[13].

Other possible benefits of Vitamin D

Apart from its benefits for immune and bone health, vitamin D also has been found to help in combination with topical minoxidil for female-pattern hair loss, as discovered in a recent study by Hassan G et al[14]. It was found that treatment with a combination of both oral vitamin D and topical minoxidil had better outcomes for female pattern hair loss as compared to either treatment options alone. Low levels of vitamin D has also been found to be associated with several diseases such as multiple sclerosis (an autoimmune disease)[15], and heart diseases[16].

How much is enough? Several sources of Vitamin D

The main indicator of vitamin D levels in your body is by taking the blood levels. The Endocrine Society recommends that adults need at least 37.5mcg to 50mcg of vitamin D to maintain an adequate level of vitamin D in the body (i.e., serum vitamin D of > 30ng/mL)[17], which is the level generally considered to be sufficient for bone and overall health in healthy adults and individuals[1]. However, it is also noted that a level of more than 50 ng/mL may be considered as harmful and is associated with adverse effects[18,19].

Some natural and dietary sources of vitamin D include cod liver oil, flesh of fatty fish (e.g., salmon, tuna), mushrooms, and certain types of red meat[20]. Also, although having sufficient sunlight is important in the production on vitamin D in your body, it is also critical to understand that overexposure may lead to detrimental effects like skin cancer as well[19].


Traditionally, vitamin D has been viewed as an important vitamin in the regulation and maintenance of bone health. Recent studies have also pointed vitamin D to be an important vitamin in boosting our bodies’ immune system. This finding may be valuable especially in this COVID-19 pandemic, with evidence to show that a sufficient level of vitamin D may be crucial in preventing severe disease of COVID-19 infection as well.


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  14. Hassan GFR, Sadoma MET, Elbatsh MM, Ibrahim ZA. Treatment with oral vitamin D alone, topical minoxidil, or combination of both in patients with female pattern hair loss: A comparative clinical and dermoscopic study. J Cosmet Dermatol. 2022 Jan 10. Available on:
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  18. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  19. Harvard T.H. Chan School of Public Health. The Nutrition Source: Vitamin D. 2022 January. Available on:
  20. Roseland JM, Phillips KM, Patterson KY, Pehrsson PR, Taylor CL. Vitamin D in foods: An evolution of knowledge. Pages 41-78 in Feldman D, Pike JW, Bouillon R, Giovannucci E, Goltzman D, Hewison M, eds. Vitamin D, Volume 2: Health, Disease and Therapeutics, Fourth Edition. Elsevier, 2018.
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