Vitamin H is another name for the vitamin more commonly known as biotin and is part of the B vitamin group. Its function in the body is to act as an essential part of certain enzymes. A deficiency in vitamin H causes hair loss, facial rashes, and nervous system symptoms. Humans cannot synthesize the substance, but foods such as eggs, meats, and some vegetables have low concentrations of the vitamin.
The enzymes that need Vitamin H for efficient functioning are involved in metabolizing fats and carbohydrates. Vitamin H deficiency is rare, according to the National Institutes of Health (NIH) in the United States, but when it does occur, it is diagnosed by unusual symptoms. These include a rash around the mouth, eyes, and nose and the presence of hair loss. Mental symptoms such as depression and hallucination are also possible, as are exhaustion and tingling in the limbs.
People at the highest risk of deficiency include those who lose weight rapidly, those who receive nutrition through a feeding tube, and people who are malnourished. Pregnant women can also suffer from slight biotin deficiency but should only take supplements under the supervision of a doctor. A lot of raw egg white in the diet can also prevent biotin absorption through the gastrointestinal tract and result in deficiency.
According to the Food Standards Agency (FSA) in the United Kingdom, vitamin H is produced by bacteria, algae, and some plants, but mammals such as humans need to get the necessary biotin through food. This vitamin is water soluble but is present in foods at lower levels than some other water-soluble vitamins. Liver is particularly rich in vitamin H compared to other sources, at a concentration of 1 milligram per kilogram of liver. This compares to a level of 0.01 mg per kg in other foods like meats in general and fruits.
Biotin requirements are not well known as of July 2011, but the Linus Pauling Institute of Oregon State University in the U.S. and the NIH state that 30 micrograms (mcg) a day for an adult man or woman appears to be sufficient for health. The FSA in the U.K. opts for a lower safety level of between 10 and 20 mcg. The NIH also warn that, as the appropriate dose is as yet unknown, consumers should be aware that an artificial dosage may carry risks. Although there is some evidence for benefits of supplementation in conditions such as hair loss, brittle nails, and diabetes, the NIH state that this evidence is not conclusive enough to warrant supplementation in these situations.