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Exercise-Induced Infertility

A balanced diet and regular exercise are essential to staying healthy and have been proven to increase fertility; however, too much exercise may actually impair your reproductive system, as well as your partner's. So how much of a good thing is too much?

During puberty, a girl first gets her period when her fat content rises above 17 percent and will cease if her body fat falls below 12 percent any time after that. This is because approximately 30 percent of a woman's estrogen comes from fat cells, so too little (or too much) can throw her hormones out of balance and affect her ability to ovulate. In fact, according to the American Society for Reproductive Medicine, low body weight accounts for just as many cases of primary infertility as obesity (6 percent of all primary infertility cases).

A body fat level just 10 to 15 percent above or below normal has been shown to cause oligomenorrhea (irregular menstruation) or amenorrhea (cessation of menstruation), which studies have shown occurs in 1 to 44 percent of athletes (compared with two to five percent in the general population), most often in ballet dancers and long distance runners. In one study published in the journal Fertility and Sterility, the estrogen levels in healthy women who began training for a marathon decreased by over 50 percent. Female athletes may also have a shortened luteal phase (less than ten days), or anovulatory cycles (in which there is still bleeding, but ovulation does not occur). Even if a female athlete continues to ovulate, the lining of her uterus may not be prepared to receive and nourish a fertilized egg because her body isn't producing sufficient ovarian hormones. Unfortunately, these conditions may be hard to detect because these women appear to be menstruating normally and their infertility may not be diagnosed until they are unable to conceive.

Strenuous exercise has also been shown to potentially affect the outcome of IVF. A study reported in the Journal of Obstetrics and Gynecology found that women who exercised four or more hours a week for years were 40 percent less likely to have a live birth after in vitro fertilization, and exercising four or more hours for one to nine years before attempting in vitro fertilization doubled the risk of implantation failure. Conversely, women who walked one to three hours a week did not increase their risk of IVF failure, but a woman who walked more than four hours a week were 50 percent less likely to have a live birth. However, the researchers add that their findings were "not strong enough to encourage women to abandon exercise and embrace a sedentary lifestyle," and that more studies are needed to confirm their findings.

Although the cause of this estrogen deficiency and menstrual irregularity in athletes is not fully understood, scientists believe that ovarian stimulation and estrogen production are decreased due to suppression of hypothalamic gonadotropin releasing hormone (GnRH) which also decreased the secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) by the pituitary gland.

However, it has been shown that exercise alone does not induce amenorrhea. The type and severity of the infertility problems experienced by over-exercisers depend on several factors, including the type of exercise, the intensity and duration of training, and the rate of progression of the training program. For instance, researchers found that normally sedentary women who took more than one year to build up to low to moderate exercise (15 to 20 miles/week) did not experience problems, but women who participated in moderate to intense training (30 to 50 miles/week) with a buildup of just two months had a higher incidence of significant menstrual abnormalities.

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