What Is It?
Vitamin D is called the sunlight vitamin because the body produces it when the sunís ultraviolet B (UVB) rays strike the skin. It is the only vitamin the body manufactures naturally and is technically considered a hormone. Essential for building strong bones and teeth, vitamin D also helps to strengthen the immune system and may prevent some types of cancer.
While just 10 to 15 minutes in the summer sun a few days a week supplies adequate amounts of vitamin D, those who canít get out in the sun may need a supplement. In winter, people in northern climes who donít get enough sun may also need additional amounts of the vitamin. Unfortunately, the bodyís ability to manufacture vitamin D appears to decline with age, so older adults may need to get more vitamin D through diet (fortified milk and fatty fish have good amounts) or supplements, whether theyíre exposed to sunlight or not.
Surprisingly, even younger adults may have inadequate stores of this nutrient: In one study involving almost 300 patients of varying ages who were hospitalized for different types of ailments, 57% were found to have low levels of vitamin D. This insufficiency occurred in a full one-third of the people who were getting the recommended amounts of vitamin D from their diet or supplements.
By promoting the absorption and balance of calcium and phosphorous in the body, vitamin D strengthens the bones and teeth and also fosters normal muscle contraction and nerve function. It is also useful for promoting immunity and blood cell formation. In addition, Vitamin D supplements may slow or even reverse some cancers.
Specifically, vitamin D may help to:
Prevent osteoporosis. The body cannot absorb calcium from food or supplements without an adequate intake of vitamin D. If calcium levels in the blood are too low, the body will steal the mineral from the bones and supply the muscles and nerves with the amount they need. Over time, the loss of calcium in the bones can lead to osteoporosis, a disease in which bones become porous and prone to fractures. 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.
In a study of 176 men and 213 women over age 65 done at Tufts University, those who took 500 mg of calcium and 700 IU of vitamin D daily for three years experienced a decrease in bone density loss. Moreover, the incidence of fractures was cut in half. In another study, of 3,270 healthy elderly French women, a daily dietary supplement of 1,200 mg calcium plus 800 IU of vitamin D lowered the incidence of hip fractures by 43% in just two years.
Protect against certain types of cancer. Some studies indicate that vitamin D may be useful in preventing cancer of the breast, colon, and prostate. In a clinical trial of 438 men, researchers reported that participants with colon cancer had lower blood levels of vitamin D than those who did not have the disease. In addition, the men with the highest intake of vitamin D were the least likely to get colon cancer. More studies are needed to support this finding and to determine if it is applicable to women.
Slow joint damage due to arthritis. 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. It did not, however, prevent the disease from developing.
Ease back pain. Individuals who are prone to back problems may benefit from taking vitamin D because of its ability to promote strong bones and cartilage.
Protect against multiple sclerosis. Preliminary animal research suggests a possible connection between high vitamin D levels and immunity to this disabling nerve disorder. This hypothesis may explain why both in the tropics (where there is ample sun to boost vitamin D levels) and in coastal Norway (where sun is scarce, but fatty fish rich in this nutrient abound and are eaten by the local population), cases of MS are rare. More studies in humans are needed, however.
Relieve the symptoms of psoriasis. 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. A few studies show that individuals with psoriasis have low levels of this vitamin. Donít bother with over-the-counter vitamin D creams and supplements, however; they have little effect on psoriasis. Studies do show that a vitamin D3 derivative (1,25 dihydroxycholecalciferol), or activated vitamin D, which is available only by prescription in cream and supplement form, may be useful for psoriasis. It is thought to work by helping skin cells to replicate normally.
Note: Vitamin D has also been found to be useful for a number of other disorders. For information on these additional ailments, see our Dosage Recommendations Chart for Vitamin D.