There is a lack of objective data about hair loss without skin shedding. At one time, there was a widespread belief that zinc deficiency is a common cause. However, zinc supplementation has not been shown to improve hair loss, even when a deficiency is suspected. One area that seems clear is that iron deficiency (a low serum ferritin without anemia) is linked to hair loss in women. In one study, 72% of women with low iron stores (a serum ferritin less than 40 mcg/l) had reduced hair density.