Vitamin D is described a fat-soluble vitamin, but it actually functions as a hormone in the body. It is produced in the skin and released into the blood to affect the bones. Its main function is to maintain levels of calcium in the blood. There is a feedback system with the parathyroid gland to produce active vitamin D3 when the body needs it, and this "vitamin" is closely related structurally to the body hormones, estrogen and cortisone. Because it can be manufactured by the body through skin exposure to the sun, it is not classed as an essential nutrient. Vitamin D, also called calciferol, has several vitamin variants, all of which are sterol (cholesterol-like) substances. Vitamin D2, or activated ergo-calciferol, is the major synthetic form of provitamin D. Vitamin D3, or cholecalciferol, is found in animals, mainly in fish liver oils. These are converted in the liver and kidneys to 25-hydroxycholecalciferol and 1, 25-dihydroxylcholecalciferol, the major circulating active forms of vitamin D.
Vitamin D is manufactured in the human skin when in contact with the ultraviolet light in the sun’s rays. The sunlight interacts with 7-dehydrocholesterol to form cholecalciferol, which is then transferred to the liver or kidneys and converted to active vitamin D. Wintertime, clouds, smog, and darkly pigmented skin reduce the body’s production of vitamin D. Vitamin D is stored in the skin, brain, spleen, and bones and prevents osteoporosis; increases bone strength; increases calcium absorption/ and is used to treat psoriasis.
Beyond calcium metabolism, vitamin D aids normal calcification of the bones in the body and influences utilization of the minerals phosphorus and magnesium. Calcium, phosphorus, and magnesium, together with other minerals make up our bones. Vitamin D3 helps increase the absorption of calcium from the gut, decreases excretion from the kidneys, stimulates reabsorption of calcium and phosphorus from bone, helps put them into teeth, and helps to maintain normal blood levels of calcium and phosphorus. Vitamin D deficiency results in rickets (in children) and osteomalacia (in adults) – both of which are characterized by a reduced level of calcium being deposited in bones and a weakening of bone strength. It also helps prevent osteoporosis.
Dietary Sources: Provitamin D is found mainly in animal foods. D3, or "natural" vitamin D, is found in fish liver oil, which is the traditional source of both A and D. Egg yolks, butter, and liver have some D, as do the oily fish, such as mackerel, salmon, sardines, and herring. Plant foods are fairly low in D, which means that strict vegetarians who do not get adequate exposure to sunlight do not get adequate amounts of vitamin D.
Dosage: The RDA for vitamin D is 400 IU per day.
Side Effects: Because vitamin D is a fat-soluble vitamin, it is stored in the body and has the potential to reach toxic levels if taken in high doses for prolonged periods of time. Intakes over 1000IU (nearly 3 times the daily value) can cause nausea, diarrhea, skin rash, headaches, muscle weakness, calcium deposits and kidney stones. It is considered by many authorities to be the most potentially toxic vitamin.
Vitamin D research shows the following:
1. Maintains calcium levels in the body
2. Reduces cancer risk
3. Controls prostate cancer
4. Reduces prostate cancer mortality
5. Reduces blood pressure
6. Improves blood glucose levels in diabetics
7. Improves glucose intolerance
8. Improves rheumatoid arthritis
9. Can improve symptoms of multiple sclerosis
10. Vitamin D deficiency affects insulin secretion and action
11. May prevent fractures in general population
12. Prevents fractures in postmenopausal women
13. Prevents hip fractures
14. Reduces risk of colorectal cancer
15. Is necessary for normal fetal growth and development
16. Increases bone density
17. Reduces risk of type I diabetes
18. Prevents ischemia-induced brain damage
19. May help prevent inflammatory bowel disease
20. May help prevent cardiovascular disease
21. Is a treatment for hyperparathyroidism
22. Contributes to death of breast cancer cells
23. Prevents rickets
24. Is treatment for psoriasis
25. Promotes tooth retention
26. Increases immune function
27. Treats seasonal affective disorder
28. Treats acne
29. Treats ichythyoses
30. Treats skin cancer
Vitamin D Abstracts (266)
Vitamin D Citations (414)