If you are a premenopausal woman with unexplained fatigue, ask your doctor about having your blood ferritin level checked. If it's 50 or less, iron supplements may help, even if you don't have anemia. Ferritin is a protein that your body uses to bind iron in tissues, so its blood level is usually a good measure of your body's iron stores. In a recent French study published in the Canadian Journal CMAJ, women between the ages of 18 and 50 who complained of fatigue and had ferritin levels below 30 were given an iron supplement (80 milligrams a day of prolonged-release ferrous sulfate) or a placebo. After 12 weeks, the iron group reported less fatigue than the placebo group. Many young women have low iron because of blood loss during menstruation. Even so, talk to your doctor before taking iron supplements.