We know the purpose of the immune system. It defends your body from invading pathogens, promotes protective immunity, and maintains tolerance to your own healthy cells.
We also know that vitamin D is crucial to our bone health primarily by making calcium more bioavailable for your body to use. Scientists are discovering that vitamin D also has a critical role in modulating your innate and adaptive immune responses. A deficiency in vitamin D is linked to a higher susceptibility to infection and a higher risk of autoimmunity. Thus, the benefits of vitamin D may extend beyond the benefits of bone and calcium homeostasis and provide benefits to people with autoimmune diseases.
Vitamin D and bone health
The most well-known benefit of vitamin D is that it promotes calcium homeostasis and bone health. It enhances the absorption of calcium in the small intestine and stimulates calcium reabsorption of bone. In addition, it promotes the mineralization of the collagen matrix in bones.
For humans, vitamin D is primarily synthesized in the skin from exposure to the sun, although that process can be influenced by season, latitude, skin pigmentation, or use of sunblock. However, vitamin D must go through a second process in the liver to form vitamin D3. Then it acts in the intestine to stimulate calcium reabsorption and promote osteoblast differentiation and matrix calcification.
Vitamin D is vital to many tissues in our bodies including cells in the bone marrow, brain, colon, breast and malignant cells, and immune cells. Thus, vitamin D has many functions other than promoting bone health. It impacts the endocrine system, and it may act in a paracrine or autocrine manner.
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