How serious is it that my iron levels are low?

Iron deficiency: Iron deficiency can cause anemia, fatigue, poor thinking, abnormal hair and nail growth, and pica (craving unusual things to eat). In a woman your age, it is usually due to the loss of blood (and the iron inside the red cells) with menstruation. Please see your doctor to determine whether anything else is causing your low iron levels, and to receive appropriate advice on iron supplementation.