Common Name: Vitamin D
Synonyms: Calciferol, calcitriol, cholecalciferol (D3), ergocalciferol (D2)

Overview:

Vitamin D is a fat-soluble vitamin. Vitamin D comes in two forms ergocalciferol or vitamin D2 and cholecalciferol, vitamin D3. Vitamin D2 comes from food sources while vitamin D3 is manufactured in the skin when it is exposed to sunlight. Until vitamin D is metabolized in the liver to 25-hydroxyvitamin D3. This form of vitamin D is also inactive until metabolized in the kidneys to produce the final vitamin D which is a pro hormone. This pro-hormone has no hormonal activity of its own. It is must be converted into the molecule that does, 1 alpha, 25-dihydroxyvitamin D . This hormone plays vital role in the: absorption of calcium and phosphorous from the intestines, in mobilizing calcium from bone, and the reabsorption of calcium by the kidneys. Because of its role as a hormone, Vitamin D is also responsible for the growth of the parathyroid gland as well as the production of the parathyroid hormone. When vitamin D levels decrease, the parathyroid hormone level increases. This leads to the reabsorption of bone. Vitamin D has also shown the ability to enhance the functioning of the immune system, helps regulate insulin secretion and plays an important role in female reproduction.
Because vitamin D is not found in many food sources, it has been added to milk and cereal to help prevent a deficiency. Vitamin D supplements are very important when sun exposure is limited. Vitamin D deficiencies are very common in people who do not drink milk or receive little sun exposure. It is very common in:

• The elderly, who tend to spend more time indoors
• Those living in northern latitudes. In fact vitamin D supplements are recommended for those who live north of the Mason Dixon line in the United States.
• People who were protective clothing or sun block in the summer time.
• People with liver problems or alcoholics
• Those with malabsorption syndromes such as Crohn’s’ disease, cystic fibrosis, and celiac disease.
• The use of certain medications that interfere with vitamin D absorption or metabolism.

The lack of vitamin D affects bone growth and development. A disease, in children, called rickets is caused by a vitamin D deficiency. Rickets results in demineralization that results in a softening and weakening of the bone. This disease was quite common in children and often resulted in severely bowed legs. In countries like the United States that fortify milk with vitamin D, rickets is rarely seen. In adults this softening and weakening of the bone is called osteomalcia and will eventually lead to reabsorption of the calcium in the bone and results in osteoporosis. Vitamin D is also involved in maintaining the immune system, normal muscle contractions, nerve and blood formation and is involved in cancer prevention.

Benefits

Vitamin D has been studied extensively. The research is in and it has shown how vitamin D improves our health.

• Several studies have found a strong association between low vitamin D levels and the incidence of osteoarthritis and bone fractures. Low levels of vitamin D have also been associated with the progression of arthritis of the knee in the participants in the Farmington study. This deterioration of the knee was documented by x-rays at various intervals in the 10 year period of the study. As the vitamin D level decreased the progression of the arthritis increased. Low vitamin D levels were associated with the loss of cartilage in the knee.

A more recent study found that a severely low level of vitamin D in post menopausal women was closely linked with fractures of the hip. The vitamin D levels were so small as to be hard to detect. Low vitamin D levels lead to an increase in the parathyroid hormone and demineralization of bone.

Still another study has sown that vitamin D may counteract the effects of corticosteroids on bone reabsorption. This is because it increases the absorption of calcium from the small intestines while at the same time inhibiting the production of the parathyroid hormone.

• Vitamin D also enhances the function of the immune system. In its active form, vitamin D enhances the functioning of monocytes (a type of white blood cell that helps destroy bacteria that enter the body). Before the advent of drugs to treat tuberculosis, cod liver oil and sunshine were used successfully to treat tuberculosis. With the new antibiotic resistant tuberculosis emerging, these old time treatments are regaining popularity.
• Vitamin D has been found to inhibit the proliferation of cells in several malignant cell lines including prostate cancer. The active from of Vitamin D suppresses in vitro (in the test tube) grown of human cancers such as colon cancer and malignant melanoma. The anti cancer activity of vitamin D is not very well understood and much research into this process in underway.
• The active form of vitamin D, 1,25-dihydrovitamin D has been found to be an effective treatment for psoriasis when used in cream form. Psoriasis is a skin disorder that involves abnormal skin growth and the development of large areas of thickened, reddish skin covered with scales.
• Vitamin D also plays a role in the treatment of SAD (seasonal affective disorder) that affects many people in northern latitudes during the winter when sunshine is at a minimum. How it works to help alleviate the depression that accompanies this disorder is not well understood.
• Researchers have found a connection between MS (multiple sclerosis) lesions and season. These researchers surmise that adequate vitamin D levels contribute to the lessening of MS lesion activity. These researchers indicate that this impressive correlation need proper clinical trials to demonstrate vitamin D’s role in reducing central nervous system lesions and the slowing of the progression of MS.
• Vitamin D supplementation is proving helpful in those taking anti seizure medication and corticosteroids. Both of these medications are known to reduce bone mass.

Dietary Sources

The sun is the best source of vitamin D. although both milk and cereals have been fortified with vitamin D, the few natural sources of vitamin D are:

	Salmon		Sardines
	Eel		Mackerel, Tuna and Herring
	Cod Liver Oil		Eggs
Milk Fortified with Vitamin D

Recommended Dosage:

The official U.S. and Canadian recommendations for daily intake of vitamin D are as follows:

• Infants 0–12 months, 200 IU (5 mcg)
• Males and females 1–50 years, 200 IU (5 mcg)
  51–70 years, 400 IU (10 mcg)
  71 years and older, 600 IU (15 mcg)
• Pregnant women, 200 IU (5 mcg)
• Nursing women, 200 IU (5 mcg)

When taken in at the recommended doses Vitamin D is considered safe. Since vitamin D is a fat soluble vitamin it can be stored in the body. Vitamin D toxicity can develop when it is taken in large amounts. Below is a list of the safe upper limits for vitamin D daily intake.

• Infants 0–12 months, 1,000 IU (25 mcg)
• Males and females 1 year and older, 2,000 IU (50 mcg)
• Pregnant and nursing women, 2,000 IU (50 mcg)

Contra-indications

• People with sarcoidosis (a condition where small lumps of tissue appear in any organ of the body including the skin) or hyperparathyroidism should never take vitamin D without first consulting a physician.
• Chronic doses that exceed 95mg or 3800I/U can lead to much calcium in the blood. Some of the symptoms of early hypercalcemia are nausea, vomiting, weakness, headaches, dry mouth, constipation, muscle and bone pain. Late symptoms of this condition are anorexia, weight loss, conjunctivitis, pancreatitis, sensitivity to light, and runny nose, the depositing of calcium in the major organs of the body, hypertension and cardiac arrhythmias.
• High doses of vitamin D to treat medical conditions should be undertaken under the supervision of a qualified healthcare practioner.
• Women who are pregnant or breastfeeding should consult a health care provider before taking a vitamin D supplement.

Drug interactions

• The following drugs can interfere with the absorption of vitamin D, Cholestyramine and Colestipol (cholesterol lowering medications), mineral oil and orlistat (a weight loss medication).
• Olestra, a fat substitute may interfere with the absorption of Vitamin D and the other fat soluble vitamins A, E, and K. Olestra has been fortified with these vitamins to make up for the decrease in the body’s ability to absorb these vitamins.
• Phenobarbital and Phenytoin may lower blood levels of vitamin D by inhibiting the metabolism of vitamin D by the liver.

References

1. http://healthlibrary.epnet.com/GetContent.aspx?token=e0498803-7f62-4563-8d47-5fe33da65dd4&chunkiid=21657
2. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminD/
3. http://www.umm.edu/altmed/ConsSupplements/VitaminDcs.html
4. http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/vit_0265.shtml

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