This page was last edited on April 15, 2021

Vitamin D is a fat-soluble steroid hormone responsible for the intestinal absorption of calcium, iron, magnesium, phosphate and zinc. In humans, dietary Vitamin D is negligible; most comes from exposure of skin to sunlight or from supplementation. Vitamin D is fat-soluble, regulates calcium levels, helps modulate the immune system, and is vital to good bone health.

Vitamin D2

Vitamin D2, known as ergocalciferol, is a vitamin D found in plants, mushrooms, and yeasts, and sometimes in foods fortified with vitamin D.[3]

Vitamin D3

Vitamin D3, known as cholecalciferol, is synthesized in the human skin from the UVB radiation in sunlight. D3 can also be obtained from supplements.[3]

VDR gene

The VDR gene, also known as nuclear receptor subfamily 1 group I member 1, provides instructions for making vitamin D receptor, which controls the body's response to vitamin D.[1] Vitamin D-dependent rickets, alopecia areata (an autoimmune disease), intervertebral disc disease, kidney stones and leprosy have all been linked to the VDR gene.[1]

Immune function

Vitamin D improves regulatory T cell function in healthy adults[4] and in patients with relapsing remitting multiple sclerosis,[5] suggesting that it may play a role in both preventing and ameliorating autoimmune disease. Experimental studies have shown that vitamin D helps protect against a proliferation of CD4+ T cells, and reduces the number of Th1 and IL-17 cytokines.[2]

Infectious disease

Vitamin D deficiency increases the risk of viral infections.[citation needed]

Epstein-Barr virus

An Epstein-Barr virus protein EBNA-3 has an affinity for the Vitamin D receptor and may actually block the activation of VDR-dependent genes by Vitamin D.[6]

Supplementation

Optimal levels

The recommended blood level of Vitamin D varies considerably by government body and health society.

The US Institute of Medicine suggests levels between 20 ng/ml and 50ng/ml.[7]

The Vitamin D Council suggests a level of 50 ng/ml or 125 nmol/l as "ideal."[8][9]

In the United States, 41.6% have serum levels below 20 ng/ml, the threshold for deficiency or 82.1% of African-Americans and 69.2% of Hispanics