Many factors account for the lack of menstrual cycles. Missed periods are caused by pregnancy, birth control pills, and stress. Travel, menopause, drugs, and hormone imbalances can also stop periods. Women with eating disorders, such as anorexia nervosa, often do not have their periods.
Athletic amenorrhea is caused by endurance training.
As many as 20 percent of racing runners do not have periods. Female athletes often skip or have no periods. This is harmless and can be reversed. Monthly periods return with weight gain and less training. Get a medical check-up to be sure no other problems are causing the missed periods.