Dr. Mark W. Mahowald responds:

There is evidence that RLS may be associated with abnormalities of iron metabolism in the central nervous system. In many cases, RLS is related to low serum ferritin levels, which may or may not be associated with low serum iron levels. (Ferritin is a protein in the body that binds to iron, and most of the iron stored in the body is bound to ferritin. The amount of ferritin in the blood shows how much iron is stored in your body.) In such cases, if taking iron supplementation normalizes the serum ferritin levels, then the RLS symptoms may improve or disappear. However, ferritin levels may remain low despite normal iron levels. If the symptoms persist despite normal ferritin levels, then RLS medication may be needed, though possibly at a reduced dosage.