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.

It also appears that proper nutrition and caloric intake during exercise plays a key role in menstrual health. Researchers at the University of Pittsburgh gave monkeys, who have menstrual cycles very similar to women, a fixed amount of food and trained them to run on treadmills. The study, published in the Journal of Clinical Endocrinology and Metabolism, found that "there were no significant changes in body weight or caloric intake over the course of training and the development of amenorrhea." Although the monkeys' body weight did not change, their metabolic hormones decreased, suggesting that the suppression of ovulation is more closely related to a "negative energy balance" than to a decrease in body weight. The researchers then provided four of the eight monkeys with additional food while maintaining their exercise program. All the monkeys eventually resumed normal menstrual cycles; however, the monkeys who increased their food consumption rapidly and consumed the most food resumed ovulation within as little as 12 to 16 days, while those who increased their caloric intake more slowly and ate less food took almost two months to resume ovulation.

Recent research has indicated that men aren't immune to exercise-induced infertility. According to a new study published in the International Journal of Sports Medicine, men who regularly work out to the point of exhaustion can suffer from lowered fertility. The study, conducted by researchers at the University of Cordoba, Spain, confirmed past research on the relationship between exhaustion, sperm count and hormone levels. Men who over-exercise and become under-weight can also experience lower sperm motility and poor sperm morphology.

In addition, men who hope to conceive should not take anabolic steroids, even if they are legal and purchased at health food stores in the form of androstenedoine. While these substances can increase muscle mass, they can also shrink testicles, lower sperm count, and cause liver disease and early heart attacks. According to the American Society of Reproductive Medicine, men and women trying to conceive should not run more than 10 miles a week, and men should not mountain bike for more than two hours, six times a week.

It is also clear that finding a healthy balance between training and diet is essential. This may involve reducing training mileage and/or increasing caloric intake. A few, very minor changes in training and diet can not only reverse amenorrhea, but have been found in studies to improve athletic performance. In fact, adding just one complete rest day per week and increasing caloric intake by as little as 350 calories per day can reverse amenorrhea in some women.

The bottom line is that the benefits of moderate, regular exercise far outweigh the risks - just be sure to eat a balanced diet, get plenty of rest, and maintain a healthy weight. And remember that any fertility changes brought about by heavy-duty exercise can be temporary. After two or three days of rest, men have been shown to normalize their sperm counts and hormone levels, and when women stop exercising or cut back on their training schedule, ovulation may resume in several months.