Vitamin D is a fat-soluble vitamin that possesses both the characteristics of a vitamin and a hormone. It is necessary for growth, especially for normal growth and development of bones and teeth in children.

It protects against muscle weakness and is involved in regulation of the heartbeat. It is also important in the prevention and treatment of breast and colon cancer, osteoarthritis, osteoporosis, and hypocalcemia. It enhances immunity and is necessary for thyroid function and normal blood clotting.

It can be found in three forms including vitamin D2 (ergocaliciferol) which comes from food sources, vitamin D3 (cholecalciferol) which is synthesized in the skin as a response to the exposure to the sun’s ultraviolet rays, and a synthetic form vitamin D5. Vitamin D3 is considered the natural form and is the most active.

Ergocaliciferol, the form we get from food, is not fully active and requires conversion by the liver and kidneys to become fully active. This is why people with liver or kidney disorders have a higher risk for developing osteoporosis.

Exposing the skin to the sun’s ultraviolet rays causes a cholesterol compound in the skin to be transformed into a precursor of vitamin D. Exposing the face and arms to the sun for fifteen minutes three times a week is an effective way to ensure an adequate amount of vitamin D for the body.

However, it has been found by researchers that the limited amount of sunlight during the winter months in the upper third of the U.S. continent cannot produce adequate amounts by exposure to sunlight. Therefore, supplementation is required to ensure adequate amounts during the winter months.

A severe deficiency of vitamin D can cause rickets in children and osteomalacia in adults. Rickets results when the lack of vitamin D affects the body’s ability to absorb calcium and phosphorus. Early signs of a deficiency include nervousness, painful muscle spasms, leg cramps, and numbness of the arms and legs.

Eventually, malformations of the bones may develop due to bone softening. Bowed legs, knock-knees, scoliosis, a narrow rib cage, a protruding breastbone, and/or beading at the ends of the ribs as well as tooth decay, delayed walking, irritability, restlessness, and profuse sweating. Fortunately, rickets is now very rare in the U.S. It is usually seen in children aged six to twenty-four months.

Vitamin D deficiency in adults is referred to as osteomalacia and is most often related to the body’s inability to properly absorb phosphorous and calcium. It is most likely to occur in pregnant women and nursing mothers, whose nutritional requirements are higher than normal, or individuals with malabsorption problems.

Osteomalacia may also affect people whose diets are extremely low in fat such that adequate bile cannot be manufactured and vitamin D cannot be absorbed. This condition can be caused by kidney failure. It is difficult to diagnose osteomalacia and it often misdiagnosed as osteoporosis.

Less severe deficiencies may result in loss of appetite, a burning sensation in the mouth and throat, diarrhea, insomnia, vision problems, and weight loss. The New England Journal of Medicine published a study which reported there are indications that vitamin D deficiency is much more widespread than previously thought. This is especially the case in older adults.

In a group of people who had few risk factors for deficiency, 57% were found to have below-normal levels of vitamin D and 67% of those who reported a vitamin D intake below the RDI had moderate to severe deficiencies.

Vitamin D should be taken with calcium and avoid mega doses of vitamin D to avoid toxicity. Toxicity can occur from taking over 65,000 international units of vitamin D over a period of two years.