Active women are less likely to have healthy, "normal" levels of iron than sedentary women. Usually active women have more healthy levels of nutrients than sedentary women, so what's the deal with the iron deficiency?
Well, here's what happens: high-impact exercises (like running, for example) ruptures some of your red blood cells (where iron is stored). The iron is then swept out of your body when you urinate. So over time, this small amount adds up.
To help keep your iron levels in the normal range, aim for about 18 milligrams of iron daily. Eat more beans, lean meat, and iron-fortified cereal.
(of course, talk with your doctor before beginning an exercise program or adding supplements to your diet)