Vitamin D: is found in three main forms, but Vitamin D3 is the usable form found in the body. D3 is absorbed by the small intestine and stored in bones, the brain, the liver, and even in skin. Vitamin D3 is also formed in the skin upon ultraviolet ray exposure.
You can see the variety of functions vitamin D has in this graphic below:
Its main function is to increase calcium absorption from the gut by stimulating the production of calcium-binding protein. Vitamin D may be helpful in fighting against cancer and multiple sclerosis. It has even been used in the treatment of psoriasis in some cases. Vitamin D is important in helping maintain a healthy gut microbiome.
Vitamin D is a hormonal vitamin, which means cells have receptor sites dedicated for vitamin D. In fact, the fact it is even called a vitamin is probably a misnomer at this point. All human cells have some attachment sites for vitamin D on their surfaces. Vitamin D is able to attach to these binding site and influence cellular activity.
While the totality of vitamin D in every organ is not yet fully understood, it is known we need it to maintain bone and blood levels of calcium and phosphorus. A deficiency of vitamin D leads to bone loss, and increases the rate of falls with fracture, especially in the elderly. We know vitamin D supports immune function because deficiencies lead to increased rates of the flu and colds.
It also regulates inflammation, decreases the rates autoimmune diseases and cancer, and promotes cellular maturation. Deficiency in vitamin D is linked to depression, and it is used in the production of neurotransmitters. Vitamin D is needed for a variety of different metabolic pathways in the body, yet many seem to not get enough of it.
Calcium is a tightly regulated substance in the body, so once calcium levels begin to rise above threshold in the body, the bones begin to absorb the excess calcium, strengthening bones.
We talk about vitamin D a bit in a podcast episode I’ll link below:
Hope this helps!