Why Does Excessive Exercise Cause Missed Periods?

Amenorrhea is the clinical term for when a female misses one or more menstrual periods. Missing a period due to excessive physical activity is a form of secondary amenorrhea called exercise-induced amenorrhea. This common and reversible disorder occurs in 5 percent to 25 percent of female athletes, depending on which type of sport they participate in.

A female gymnast is on the mat. (Image: Jupiterimages/Stockbyte/Getty Images)

How a Normal Period Begins

The endocrine and reproductive systems work in tandem to perpetuate a normal menstrual cycle. In the brain, the hypothalamus excretes a hormone called gonadotropin releasing hormone, or GnRH. GnRH signals the pituitary gland to excrete two hormones that are necessary to have a period: leutinizing hormone, LH, also called lutropin, and follicle stimulating hormone, or FSH. Lutropin signals your ovaries to release an egg after FSH causes that egg to reach maturity.

Hormonal Interruption

Normally, the hormone GnRH is released in a pulsing sequence once every 60 to 90 minutes. However, an intense training schedule stresses the body in such a way that it interrupts this normal pulsating release of GnRH. Vigorous training may either cause the hormone to be released less frequently or it may cause the amount of the hormone released at each pulse to decrease. Amenorrhea is even more likely to occur when excessive exercise is combined with low calorie intake or a low body fat percentage. Menstrual cycles can resume normally after you reduce the intensity of your training schedule or increase your calorie intake and body weight.

Normal Vigorous Exericse

It's not necessary to discourage vigorous exercise in order to avoid amenorrhea. In fact, vigorous exercise should be encouraged as a part of a normal healthy lifestyle to promote general health and well-being. The American College of Sports Medicine recommends at least 30 minutes of moderate physical activity or at least 20 minutes of vigorous exercise on most, if not every day of the week. However, it's not necessary to do more than 60 minutes of cardiovascular exercise each day. In fact, going beyond an hour of aerobic activity can do more harm than good. It can create an energy shortage in your body that disrupts normal metabolic and hormonal functioning.

Long-Term Risks of Amenorrhea

Occasionally missing a period is not necessarily dangerous, but long-term amenorrhea can be. Over time, the hormonal changes associated with not having a period may lead to heart disease, infertility and changes in bone density, leading to fractures. If you are experiencing missed periods, you should consult your doctor. Be sure to discuss the specifics of your current training and eating regimen. Excessive exercise is only one of the causes of secondary amenorrhea, so do not rule out other possible medical issues, even if you are currently following an intense training schedule.