Vitamin D : Health Benefits

by MedlinePlus

Vitamin D is found in numerous dietary sources such as fish, eggs, fortified milk, and cod liver oil. The sun is also a significant contributor to our daily production of vitamin D, and as little as 10 minutes of exposure is thought to be enough to prevent deficiencies. The term "vitamin D" refers to several different forms of this vitamin. Two forms are important in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized by plants. Vitamin D3 is synthesized by humans in the skin when it is exposed to ultraviolet-B (UVB) rays from sunlight or the diet.

The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Recently, research also suggests vitamin D may provide protection from osteoporosis, hypertension, cancer, and several autoimmune diseases.

Deficiency: Rickets and osteomalacia are classic vitamin D deficiency diseases. In children, vitamin D deficiency causes rickets, which results in skeletal deformities. In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones. People who are at a high risk for vitamin D deficiencies are the elderly, dark skinned, obese, exclusively breast-fed infants, and those who cover all exposed skin or use sunscreen whenever outside. Also, those who have fat malabsorption syndromes (e.g., cystic fibrosis) or inflammatory bowel disease (e.g., Crohn's disease) are at risk.

Adequate Intake (AI): AI levels have been established by the U.S. Institute of Medicine of the National Academy of Sciences to prevent deficiencies in vitamin D. The AI is 5 mcg (200 IU) daily for all individuals (males, female, pregnant/lactating women) under the age of 50-years-old, 10 mcg daily (400 IU) for all individuals from 50-70 years-old, and 15 mcg daily (600 IU) for those who are over the age of 70-years-old. The daily "upper limit" for vitamin D is 25 mcg (1,000 IU) for infants up to 12 months of age and 50 mcg (2,000 IU) for children, adults, pregnant, and lactating women due to toxicities that can occur when taken in higher doses. The most effective way at ensuring adequate vitamin D levels is to take a daily multivitamin, which contains 400 IU.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Uses based on scientific evidence

Familial hypophosphatemia

Familial hypophosphatemia is a rare inherited disorder characterized by impaired transport of phosphate and diminished vitamin D metabolism in the kidneys Familial hypophosphatemia is a form of rickets. Taking calcitriol or dihydrotachysterol orally in conjunction with phosphate supplements is effective for treating bone disorders in people with familial hypophosphatemia. Management should be under medical supervision.

Fanconi syndrome-related hypophosphatemia

Fanconi syndrome is a defect of the proximal tubules of the kidney, and is associated with renal tubular acidosis. This syndrome classically is characterized by a kidney loss of bicarbonate and multiple electrolytes, including phosphate and calcium. In Fanconi syndrome, the defect also is associated with a decrease in vitamin D synthesis by the proximal tubule. Taking ergocalciferol orally is effective for treating hypophosphatemia associated with Fanconi syndrome.

Hyperparathyroidism due to low vitamin D levels

Some patients may develop secondary hyperparathyroidism due to low levels of vitamin D. The initial treatment for this type of hyperparathyroidism is vitamin D. For patients with primary or refractory hyperparathyroidism, surgical removal of the parathyroid glands is commonly recommended.

Hypocalcemia due to hypoparathyroidism

Hypothyroidism (low blood levels of parathyroid hormone) is rare, and is often due to surgical removal of the parathyroid glands. Low levels of calcium (hypocalcemia) and low levels of phosphorus may occur. Oral doses of dihydrotachysterol (DHT), calcitriol, or ergocalciferol at high doses can assist in increasing serum calcium concentrations in people with hypoparathyroidism or pseudohypoparathyroidism.

Osteomalacia

Although adult bones are no longer growing, they are in a constant state of turnover. In adults with severe vitamin D deficiency, bone mineral is lost ("hypomineralization") and results in bone pain and osteomalacia (soft bones). Osteomalacia may result from deficiency of vitamin D in elderly patients, decreased absorption of vitamin D, patients with chronic malabsorption syndrome secondary to jejunoileal bypass, patients with partial gastrectomy, aluminum-induced bone disease, chronic liver disease, or kidney disease with renal osteodystrophy.Treatment for osteomalacia depends on the underlying cause of the disease and often includes pain control and orthopedic surgical intervention, as well as vitamin D and phosphate binding agents. Reduction of exposure to excess iron or aluminum, and treatment with aluminum chelating agents to reduce aluminum toxicity may be necessary. Blood calcium and phosphorus levels should be followed closely.Oral calcifediol is effective for treating osteomalacia secondary to liver disease (hepatic osteodystrophy), and anticonvulsant-induced osteomalacia. Ergocalciferol is effective for osteomalacia due to malabsorption syndromes and corticosteroid-induced osteomalacia.

Psoriasis

A number of different approaches are used in the treatment of psoriasis skin plaques. Mild approaches include light therapy, stress reduction, moisturizers, or salicylic acid to remove scaly skin areas. For more severe cases, treatments may include UV-A light, psoralen plus UV-A light (PUVA), retinoids such as isotretinoin (Accutane), corticosteroids, or cyclosporine (Neoral, Sandimmune). The synthetic vitamin D3 analog calcipotriene (Dovonex) appears to control skin cell growth and is used for moderately severe skin plaques, particularly for skin lesions resistant to other therapies or located on the face. Topical derivatives of cholecalciferol have also been used either alone or in combination with other agents (such as topical corticosteroids). Calcitriol 3 mcg/gram ointment has been studied and reported as safe and efficacious as an alternative to calcipotriol 50 mcg/gram ointment, administered with corticosteroids followed by a cholecalciferol maintenance monotherapy. Vitamin D3 (tacalcitol) ointment 4 mcg/grams used once daily for six months has been reported as being safe and well-tolerated.

Rickets

In infants and children, vitamin D deficiency results in the failure of bone to mineralize. Other rare causes include calcium or phosphorus deficiency. Rapidly growing bones are most severely affected by rickets. In severe cases, low serum calcium levels (hypocalcemia) may cause seizures. Rickets used to be common but is rarely seen now that countries have adopted the practice of fortifying milk with vitamin D. Ergocalciferol or cholecalciferol is effective for treating vitamin D deficiency rickets, and may be administered gradually over 2-3 months, or in an accelerated one-day dosing regimen. Calcitriol should be used in patients with renal (kidney) failure. Treatment should be under medical supervision.

Muscle weakness/pain

Vitamin D deficiency has been associated with muscle weakness and pain in both adults and children. Limited research has reported vitamin D deficiency in patients with low-back pain, and supplementation with 5,000-10,000 IU of vitamin D per day leading to pain reduction in many patients after three months. A randomized controlled trial found that supplementation of elderly women with 800 IU/day of vitamin D and 1,200 mg/day of calcium for three months increased muscle strength and decreased the risk of falling by almost 50% compared to supplementation with calcium alone.

Osteoporosis

Osteoporosis is a multifactorial disease, and vitamin D deficiency can be a contributing factor. Without sufficient vitamin D, calcium absorption cannot be maximized and the resulting elevation in parathyroid (PTH) secretion by the parathyroid glands results in increased bone resorption, which may weaken bones and increase the risk of fracture. Vitamin D supplementation has been demonstrated to slow bone loss and reduce fracture, particularly when taken with calcium. To prevent fractures, 400-800 IU of vitamin D has been recommended for adults, especially those not exposed to sunlight.

Renal osteodystrophy

Renal osteodystrophy is a term which refers to all of the bone problems that occur in patients with chronic kidney failure. The underlying cause is retention of phosphate in the body by the kidneys, leading to low calcium levels in the blood, and increased activity of the parathyroid glands (hyperparathyroidism). This, in turn, results in breakdown and weakening of bones (demineralization). Oral calcifediol or ergocalciferol may help manage hypocalcemia and prevent renal osteodystrophy in people with chronic renal failure undergoing dialysis.

Anticonvulsant-induced osteomalacia

Supplementation with vitamin D2 has been reported to reduce seizure frequency in initial research. Further study is needed to confirm these results.

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