A sensitive way to check total body iron stores is to measure the amount of ferritin in the blood. Ferritin is a protein that plays an important role in iron storage. As a general rule, the less ferritin in the blood, the less iron a body has stored up.

Cotsarelis and Trost say that what most doctors consider to be a normal ferritin level is, in fact, too low. Ferritin levels of 10-15 ng/mL are within the "normal" range. Cotsarelis says a ferritin level of at least 50 ng/mL is needed to help replenish hair. Trost and Bergfeld shoot for 70 ng/mL.

"Doctors see ferritin levels in the normal range, and don't do anything," Cotsarelis says. "But the normal range is wrong, I think. The normal range for women is 10-120 ng/ML, and for men it is 30-250 ng/mL. Why should a man's be lower than a woman's? Mostly because women are iron deficient. It is almost a public health problem. Hair loss is only an indication of this."