One large egg contains up to 25 micrograms of biotin, nearly a day’s worth for an adult. Raw egg white has a protein that inhibits the absorption of the vitamin, but cooking the egg white inactivates the protein.

Admit it. You’ve never heard of biotin. But just try to live without this water-soluble B vitamin. Also known as B7, biotin is a vitamin needed by all living organisms, but it’s only produced by bacteria, yeasts, molds, algae and some plants. Fortunately, most Americans get plenty of biotin in their diet and can recycle much of the biotin in their bodies.

Researchers have found biotin deficiencies in people who have been fed intravenously for long periods of time or who regularly consumed raw egg whites. Egg yolks are rich in biotin, but egg whites contain avidin, a protein that binds to biotin and prevents its absorption. Cooking the egg white, however, deactivates the avidin.

Biotin is needed for certain enzymes in the body to work properly, and without it individuals can experience hair loss and a scaly red rash around their eyes, nose, mouth and genital area. People with liver problems might have trouble processing biotin, and pregnancy appears to increase biotin requirements to support cell division in the fetus.

Lacking the scientific evidence to establish a recommended daily amount, the Institute of Medicine set an adequate intake level for biotin, assuming that current average levels are sufficient.

— Markian Hawryluk, The Bulletin

Daily adequate intake, in micrograms:

Adults (19+): 30 mcg

Breast-feeding women: 35 mcg

Children (0-6 months): 5 mcg

Children (7-12 months): 6 mcg

Children (1-3 years): 8 mcg

Children (4-8 years): 12 mcg

Children (9-13 years): 20 mcg

Teens (14-18 years): 25 mcg

Good sources:

Bread (whole-wheat, 1 slice): 0.02–6 mcg

Egg (cooked, 1 large): 13-25 mcg

Cheese (cheddar, 1 ounce): 0.4–2 mcg

Liver (cooked, 3 ounces): 27–35 mcg

Pork (cooked, 3 ounces): 2–4 mcg

Salmon (cooked, 3 ounces): 4–5 mcg

Avocado (one whole): 2–6 mcg

Source: Linus Pauling Institute