8 Surprise Reasons You're Still Tired

Ten percent of women are iron deficient, and half of those will develop anemia. When red blood cells aren't able to deliver enough oxygen to all the cells in the body, we feel fatigued, weak and irritable. You've probably heard that you can become iron deficient by not eating enough red meat, but that's only part of the story, says Nancy Berliner, MD, chief of Hematology at Boston's Brigham and Women’s Hospital. The most common cause of iron-deficiency anemia is blood loss, usually because of heavy periods or childbirth, and even a steady hamburger habit can't compensate for that. Distance runners are also at risk, Berliner says, because the repetitive impact on pavement can cause red blood cells to be damaged or even destroyed. If a blood test shows red-blood-cell count is too low, your doctor will probably prescribe iron supplements. (Berliner suggests 325 mg, two to three times per day.)