What is Vitamin D?

What is Vitamin D?

Vitamin D, also known as “calciferol”, is a molecule necessary for human life. It facilitates calcium absorption in the gut, reduces inflammation, contributes to cell growth and a healthy immune system, and can help prevent cancer, among other functions. It is a fat-soluble vitamin, which means it is dissolved in fat within the gastrointestinal tract, and ideally ingested with a fat-containing meal to promote absorption. Unlike water-soluble vitamins, excess fat-soluble vitamins in the body cannot be excreted via urination.

Vitamin D has two main forms; Vitamin D2 (Also known as ergocalciferol), and Vitamin D3 (Also known as cholecalciferol). They differ in their side-chain chemical structure but have similar effects within the body. The recommended daily intake of Vitamin D for adults is approximately 15 mcg (600 IU), regardless of gender or pregnancy status. The majority of Americans do not meet the minimum recommended daily intake of Vitamin D. 

Data from 2013-2016 suggested that 94% of people age one or above ingested less than 10 mcg (400 IU) from foods and beverages daily. However, 26% of the study participants did take a supplement containing Vitamin D.


Deficiency in this vitamin can cause ailments primarily relating to weakened bone structure, such as rickets in children, osteomalacia, and osteoporosis in the elderly. It may also contribute to depression, cardiovascular disease, and asthma. 

Diets most at risk of deficiency are lactose-intolerant, ovo-vegetarians, and vegans. Breastfed infants can also be at risk of Vitamin D deficiency since human milk alone does not usually allow them to meet their recommended daily allowances. Older adults can have trouble synthesizing the vitamin via sunlight and require supplementation. Individuals with limited sun exposure due to various factors may also require supplementation.


Vitamin D is synthesized endogenously by the human body when ultraviolet rays from sunlight are absorbed by the skin. Dietary sources are scarce in nature, but they include mushrooms, various types of fish (salmon, tuna, trout, mackerel), egg yolks, cheese, beef liver, and other fortified foods and beverages. 

Mushrooms are invariably the best source of Vitamin D for vegans, although it can also be found in fortified soy, almond, and oat milks. Mushrooms such as chanterelle, shiitake, maitake and oyster contain high levels of Vitamin D when exposed to sunlight, and are therefore good natural sources of this essential vitamin. 



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