The connection between vitamin D and hair loss in humans is tentative. Several studies on animals have failed to provide evidence suggesting a link in humans. Research using hairless mice shows that vitamin D protects against hair loss caused by chemotherapy administered during cancer treatment, but the results have not been replicated in humans. Experiments on mice reveal that vitamin D also plays an important role in hair re-growth, but experts say more study is needed to prove a link between vitamin D and hair loss in people.
A deficiency of vitamin D cannot be ruled out as a cause of hair loss, but no definitive data exist to show vitamin D and hair loss in humans are connected. Likewise, research does not prove that an overabundance of the vitamin leads to or prevents alopecia in people. Alopecia is the clinical term for hair loss in men and women.
Researchers seeking a connection between vitamin D and hair loss in one study discovered hair loss was prevented in mice exposed to high levels of the vitamin after treatment with a cocktail of chemotherapy agents. The study concluded that vitamin D therapy may depend on the specific chemicals used in chemotherapy and the level of vitamin D administered. Similar chemical mixtures and the potent levels of vitamin D used in animal experiments have not been tested on people.
Alopecia normally affects hair on the head but can lead to hair loss all over the body. Some people who develop the condition notice hair loss is more severe on one side of the head. Although men and women suffer from alopecia, it differs from baldness typically seen in men, which often runs in families. A weakened immune system could induce alopecia in humans, and the condition may be related to genes passed from parents to offspring.
Despite the lack of clinical evidence connecting vitamin D and hair loss, some vitamin distributors tout supplements for hair loss. Although experts do not recommend such supplements, vitamin D is necessary to support the absorption of calcium. The body makes vitamin D after exposure to sunlight, but people who live in sunny climates might still be deficient in the vitamin. Vitamin D is also found in certain foods, including dairy products, cereals fortified with extra vitamins, and fish.
Vitamin D deficiency could result in osteoporosis, especially in women after menopause, and precipitates rickets in children. Too much of the vitamin can also be harmful. Excess amounts of vitamin D can create calcium deposits in the heart or lungs. The development of kidney stones might also be caused by excessive vitamin D.