Essential things you should know about vitamin D

Vitamin D

With the start of this decade, people became a little more cautious about immunity, lifestyle, and food habits as a preventive measure to withstand the covid 19 pandemic. It is good news as people are getting aware of healthy living, and at the same time, a lot of fake news and misconception is also grasping people’s minds which has an ill effect in the long run. One such topic is vitamin D.


Vitamin D is a fat-soluble vitamin that exists in two forms – vitamin D2 (plant source)and vitamin D3 (animal source). It exists in 7 – dehydrocholesterol form which gets converted to the active form of vitamin d3 (1,25-dihydroxyvitamin D3 [1,25(OH)2D3] ) in our body through different metabolic pathways. Later, these synthesized forms are hydroxylated in the liver and kidney and are circulated in the bloodstream. Research has shown that vitamin D is an important bioregulator for maintaining calcium homeostasis in our body.

However, studies prove the role of vitamin D is more like a hormone than a vitamin. So, it is also called a hormone. It is primarily produced in the epidermal layer of skin when exposed to sunlight (UV-B rays). So, it is nick-named as “sunshine vitamin”. The preform of vitamin D3, under the skin either gets isomerized or photolysed to active forms which is then received by vitamin D receptors(VDR).  

The use of sunscreens may inhibit the UV absorption. Fair-skinned people can absorb more UV radiation compared to dark-skinned people as the former possess less melatonin( which acts as a barrier in absorption) than the latter. Sunlight deprivation can cause vitamin D deficiency. Older people who do not go out much and have less capacity to synthesize Vit D on their own can develop hypovitaminosis.

We derive around 90% of vitamin D from our body in the presence of sun rays. dietary sources of vitamin D are very selective like- cod liver oil, animal liver, fatty fishes, fortified foods, egg yolk etc. Animal-derived vit D is better absorbed than plant sources.


Vitamin D has been known for its regulatory action in maintaining bone health and calcification. But it also plays a crucial role in boosting immunity against viral infections, respiratory ailments, inflammations etc. It acts as an immunomodulator and has a role in gene expression.

In the past, tuberculosis patients were treated by exposure in sunrays and feeding cod liver oil. Later, extensive research brought the link between low vitamin levels and upper respiratory ailments.

Research shows vitamin D has a direct and indirect influence on our immune system against viral infections. The defence cells like macrophages, lymphocytes, B-cells, T-cells produce vitamin D receptors(VDR) and enzymes for vitamin D synthesis. Vitamin D stimulated production of Cathelicidin shows antimicrobial property thus supporting our innate immunity.

The effect of vitamin D reduces the action of pro-inflammatory cytokines and promotes the release of anti-inflammatory cytokines thus reducing cytokine storms that occur in any viral infection and balances the immune response. It also helps in cell proliferation and differentiation resulting in major therapeutic effects in treating metabolic diseases.

Thus, when we catch a cold or any viral infection, vitamin D acts as physical barriers or acts through the adaptive immune system to reduce the risk.

Studies showed a connection between low vitamin D content and the severity rate of respiratory or viral diseases. Low levels of vitamin D is responsible for inflammatory cytokines. Several meta-analyses of random trials showed supportive data on low vit d serum levels and the development of acute respiratory illness. Though it is a controversial topic, especially in the midst of a pandemic, research is going on to understand the mechanism of vitamin D  in detail. It also regulates RAS. Thus, low vit d may lead to CVD, diabetes, hypertension etc. 


 The novel coronavirus is rapidly mutating and spreading all over the world and the precautions are still undercover. The world is desperately in search of preventive measures which can reduce the severity of the disease. 

Covid 19 can target the upper and lower epithelial cells of the lungs by anchoring its spike protein to angiotensin-converting enzyme 2 (ACE2) which is an important enzyme for regulating the Renin-Angiotensin system (RAS) to maintain vascular balance and blood pressure making the chances of comorbidity more intense. 

It is also associated with cytokine storms developing ARDS and inflammation. 

There are some good reasons to hypothesize that vitamin D can prevent covid as it has both anti-inflammatory cytokine effect, antimicrobial effect for the early and post-covid situation. In several studies, it has an immunopathological anti-inflammatory effect in respiratory diseases. Thus it may reduce the cytokine storm. 

A series of studies has shown vitamin D has some contributions towards Covid 19. A study from Spain with 216 covid positive patients concluded that 80% were deficient. Whereas many studies found no evidence to support the fact that vitamin D can cure Covid. But low levels of vitamin D can enhance the severity. 

In Dec 2020,  the National Institute for Health and Care Excellence (NICE), in collaboration with Public Health England and the Scientific Advisory Committee on Nutrition issued a guideline on vitamin D. In the guideline, they advised taking vitamin D supplements, especially in winters. 

It is suggested to provide supplementation depending on the need to reduce the deficiency in the population especially for people who live in cold countries, old people who have decreased vitamin D productivity, or severe deficiency. 


The recent recommended dietary allowances (RDA) for the Indian population has suggested an increased intake emphasizing outdoor physical activity to derive adequate vitamin D in this tropical climate. For adults and children, an RDA of 600IU/day is advised and for infants(0-12 months) 400IU/day is suggested. It is also suggested to provide vitamin D drops up to one year of age.

The tolerable upper limit for adults and adolescents is 4000IU/day, for infants 1000 IU/day (0-6 months) and 1500 IU/day (6-12 months), for children 2500 IU/day (1-3 yrs) and 3000 IU/day (4-9yrs). Above this tolerable limit, there is a chance of toxicity and hypervitaminosis. 


Nutrition along with medicines play a significant role to combat Covid. Extensive research is going on to evaluate the potential of vitamin D. Until then we need to ensure proper vitamin D supply along with other nutrients like vit c, zinc etc. Self-medication is not advised. It is always safe to ask a doctor for the need of supplementation.  Overdose of Vit D may lead to hypervitaminosis or toxicity. 

If you are suffering from post-COVID troubles you can read about it here.

~Article by Ishita Chandra, BSc Food and Nutrition.


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