Vitamin D (calciferol) review
- Basics: a group of steroid molecules, also called the sunlight vitamin, the only vitamin the body manufactures naturally.
- Benefits: vital for the control of the levels of calcium in the blood, essential for building strong bones and teeth, helps strengthen the immune system and may prevent some types of cancer.
- Dosage: 200 IU per day for adults, 400 IU per day for pregnant women and children under the age of 10 years.
- Sources: green peppers, citrus fruits and juices, strawberries, tomatoes, broccoli, turnip greens and other leafy greens, sweet and white potatoes.
- Deficiency: sunlight, milk, fatty fish, cod liver oil, fish liver oil, egg yolks.
- Overdose: vitamin D toxicity causes nausea, vomiting, poor appetite, constipation, weakness, and weight loss.
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Vitamin D actually refers to a group of steroid molecules. Vitamin D (calciferol) is named according to the revised rules of the International Union of Pure and Applied Chemists (IUPAC). Because vitamin D is derived from a steroid, the structure retains its numbering from the parent compound cholesterol. There are two forms of the vitamin. Vitamin D2 (ergocalciferol) is derived from ergosterol in the diet, whereas vitamin D3 (cholecalciferol) is derived from cholesterol via 7-dehydrocholesterol. Vitamin D3 (cholecalciferol) is found in animal skin, and vitamin D2 (ergocalciferol) is found in yeast.
Cholecalciferol is generated in the skin of animals when light energy is absorbed by a precursor molecule 7-dehydrocholesterol. Plants synthesize ergocalciferol, which also has vitamin D activity in humans.
Vitamin D is called the sunlight vitamin because the body produces it when the sun’s ultraviolet B (UVB) rays strike the skin. It is the only vitamin the body manufactures naturally and is technically considered a hormone. Vitamin D is important for the proper absorption of calcium from food. It is vital for the control of the levels of calcium in the blood and also controls the rate at which the body excretes calcium in the urine. The active form of the vitamin is calcitriol which is synthesized from either D2 or D3 in the kidneys. Calcitriol binds to a protein transcription factor which then regulates gene expression. Essential for building strong bones and teeth, vitamin D also helps to strengthen the immune system and may prevent some types of cancer.
Vitamin D (calciferol) functions, uses, and health benefits
Vitamin D and osteoporosis – Adequate amounts of vitamin D is necessary for preventing bone loss. Low levels of vitamin D and insufficient sunlight exposure are associated with osteoporosis. The body cannot absorb calcium from food or supplements without an adequate intake of vitamin D. After menopause, women are particularly at risk for developing this condition.
Vitamin D taken along with calcium plays a critical role in maintaining bone density. Vitamin D functions by increasing the uptake of calcium from the intestine through interaction with the parathyroid glands in controlling bone resorption and serum calcium levels. Vitamin D also increases reabsorption of phosphate by the kidney tubule, and may directly affect the osteoblast, the cell which forms bone.
Vitamin D and cancer – Vitamin D’s immunomodulatory abilities may also play a role in its anti-cancer activity. Vitamin D demonstrats a dose-dependent inhibition of cell proliferation in a number of cancer cell lines. It also has a pro-differentiation effect on these cells, resulting in potent anti-cancer activity in some preliminary work. vitamin D increases the potency of cytokines and enhances the phagocyte activity and antibody-dependent cytotoxicity of macrophages and that it boosts natural killer cell activity and helps regulate T cells, among other things. Vitamin D’s analogues show significant experimental activity against colorectal, renal cell, breast and prostate cancers, among others.
Vitamin D and autoimmune diseases – Maintaining sufficient vitamin D levels may help decrease the risk of several autoimmune diseases such as insulin-dependent diabetes mellitus, multiple sclerosis, and rheumatoid arthritis. A daily multi-vitamin supplement containing vitamin D may reduce the risk of developing multiple sclerosis. Low intakes of vitamin D may be linked to an increased risk of arthritis of the hip in older women. One recent study showed that taking 400 IU or more of vitamin D daily was effective in delaying or stopping the progression of osteoarthritis of the knees. Autoimmune responses are mediated by immune cells called T cells. The biologically active form of vitamin D can modulate T cell responses, such that the autoimmune responses are diminished.
Vitamin D and psoriasis – Vitamin D is sometimesused in the treatment for psoriasis. Because vitamin D and its analogues are potent antiproliferative agents for keratinocytes and stimulators of epidermal cell differentiation. Calcipotriol has been demonstrated to significantly improve psoriatic lesions in a number of double-blind, placebo-controlled trials. Because it plays a role in skin cell metabolism and growth, vitamin D may be helpful in treating the itching and flaking associated with this skin ailment.
Vitamin D and other bone disorders – Vitamin D protects against the preventable bone diseases rickets and osteomalacia (softening of the bones in adults caused by inability to properly deposit calcium). An adequate level of Vitamin D in the body is necessary to maintain strong bones and to help prevent fractures in older people. Vitamin D supplements are also used for people with genetic diseases that interfere with the metabolism of Vitamin D.
Vitamin D (calciferol) dosage, intake, recommended daily allowance (RDA)
Supplemental vitamin D is available as vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). The recommended dietary allowance (RDI) for vitamin D is 200 IU per day for adults and 400 IU per day for women who are pregnant or lactating and for children under the age of 10 years. One IU of vitamin D is equivalent to biologic activity of 0.025 mcg of pure crystalline vitamin D3 (cholecalciferol).
Patients on glucocorticoid therapy may need extra vitamin D. For teenagers and adults, the tolerable upper intake level (UL) of vitamin D is 2000 IU per day. Pharmaceutical preparations containing 50,000 IU (1,250 micrograms) of vitamin D2 are used in the treatment of vitamin D deficiency in the elderly and in those with malabsorption syndromes, nephrotic syndrome and hepatic failure. The RDA standard is 10 mcg, or 400 international units (IU), of cholecalciferol daily for children and for women during pregnancy and lactation.
Sources of vitamin D (calciferol)
Vitamin D3 is synthesized in the skin from 7-dehydrocholesterol via photochemical reactions using ultraviolet B (UV-B) radiation from sunlight. Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin. Vitamin D2 is derived from fungal and plant sources. Vitamin D3 is derived from animal sources. Sunlight is the primary source (food is not the primary source) by converting 7-dehydrocholesterol (in the skin) to vitamin D3. Fortified foods are the major dietary sources of vitamin D. Good food sources of vitamin D include milk, fatty fish such as salmon and mackerel, cod liver oil, fish liver oil, some breads and cereals and egg yolks. Most vitamin D supplements available without a prescription contain cholecalciferol (vitamin D3). Multivitamin supplements for children generally provide 200 IU (5 mcg) and multivitamin supplements for adults generally provide 400 IU (10 mcg) of vitamin D.
Vitamin D (calciferol) deficiency
In adults, vitamin D deficiency may result in a softening of the bones known as osteomalacia. In children, vitamin D deficiency is called rickets and causes a bowing of bones not seen in adults with vitamin D deficiency. Vitamin D deficiency is characterized by inadequate mineralization or demineralization of the skeleton. Inadequate mineralization of the skeleton is the cause of rickets in children (vitamin D is also known as the antirachitic factor), while demineralization of the skeleton results in osteomalcia in adults. Further, vitamin D deficiency in adults can lead to osteoporosis. This results from a compensatory increase in the production of parathyroid hormone resulting in resorption of bone.
People who get little exposure to sunlight are most at risk of vitamin D deficiency. Vitamin D deficiency can be caused by conditions that result in little exposure to sunlight. Vitamin D deficiency in the winter is more common than previously thought and is even found in men who receive plenty of sun exposure in the summer. Those with chronic liver disease, cystic fibrosis, Crohn’s disease, Whipple’s disease and sprue are prone to vitamin D deficiency. Others at risk for vitamin D deficiency, include those that do not drink milk and who do not receive much sunlight, those who live in regions where they receive little natural light and alcoholics.
Vitamin D (calciferol) overdose, toxicity, side effects
There is a high health risk associated with consuming too much vitamin D. Taking too much vitamin D (more than 1,000 IU daily) can cause a number of adverse effects including excessive thirst, metal taste, poor appetite, weight loss, bone pain, tiredness, sore eyes, itching skin, vomiting, diarrhea or constipation, a need to urinate, and muscle problems. Vitamin D toxicity can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss.
An excess of vitamin D increases the absorption of calcium which leads to high levels of calcium in the blood and result in increased calcium absorption from the intestinal tract. Long-term overconsumption of vitamin D at any dose greater than 1,000 IU day may cause high blood pressure and premature hardening of the arteries. Vitamin D toxicity (hypervitaminosis D) induces abnormally high serum calcium levels (hypercalcemia), which could result in bone loss, kidney stones, and calcification of organs like the heart and kidneys. The hypercalcemia associated with hypervitaminosis D may cause multiple debilitating effects. Anorexia, nausea and vomiting have been observed in hypercalcemic individuals treated with 1,250 to 5,000 micrograms (50,000 to 200,000 IU)/day of vitamin D.