The molecule known as vitamin D is actually a steroid hormone, and unlike other vitamins, your body can synthesize it as long as you have adequate exposure to sunlight. Although vitamin D is very important for bone health, it also regulates a wide variety of other functions in the body.
Calcium Metabolism
The most well-known function of vitamin D is its role in regulating calcium metabolism. Blood levels of calcium must be tightly controlled in order for the nervous system to function properly. Vitamin D is essential for maintaining blood calcium levels. When calcium concentrations are low, the parathyroid gland secretes parathyroid hormone, or PTH, which activates vitamin D in the body. This active form of the molecule affects multiple organs in the body. It increases calcium absorption in the small intestine, reduces calcium excretion in the kidneys and promotes the release of calcium from bone.
Bone Growth and Maintenance
When your body does not have enough vitamin D, it cannot maintain blood calcium levels and produces more PTH, which promotes bone breakdown. In children whose bones are still growing, vitamin D deficiency causes rickets, a condition in which bones do not form correctly. In adults, it causes osteomalacia, which softens the bones and increases risk of fracture.
Immune Function
Vitamin D affects the immune system by interacting with some types of cells to dampen the immune response. This can be beneficial in cases where the immune system is over-reactive, as in autoimmune diseases. Examples of autoimmune disease include type 1 diabetes, multiple sclerosis and rheumatoid arthritis. Some studies have found that people living in regions with more sunlight have lower rates of these diseases, but it is not clear whether higher vitamin D levels are responsible.
Cell Division
Vitamin D also reduces replication in some cells. Because of this effect, it is an effective and widely used therapy for psoriasis, a condition in which skin cells multiply too quickly and form red, itchy and flaky patches of skin. Because cancer is the result of uncontrolled cell growth and division, it is possible that vitamin D may also play a role in preventing some cancers. However, evidence for vitamin D as a tool for cancer prevention or treatment is still limited. Although some studies have suggested that people with higher vitamin D intakes have lower risk of colorectal and breast cancers, not all studies have confirmed this finding.
References
- Colorado State University; Pathophysiology of the Endocrine System: Vitamin D (Calcitriol); R. Bowen; April 2010
- Linus Pauling Institute; Vitamin D; Jane Higdon and Victoria Drake; January 2008
- "American Journal of Clinical Nutrition"; Sunlight and Vitamin D for Bone Health and Prevention of Autoimmune Diseases, Cancers, and Cardiovascular Disease; Michael F. Holick; 2004
- PubMed Health; Psoriasis; November 2010
- National Cancer Institute: Vitamin D and Cancer Prevention: Strengths and Limits of the Evidence
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