How Exercise Affects Fertility

Two female readers have written me, asking if exercises can damage one's reproductive system.

"I am 34 years old and have been attending aerobics classes in the gym. I am planning to get pregnant this year and I am concerned that the strenuous exercise will minimize my chance of getting pregnant. I also want to trim down my body fat (especially in the abdomen) but I know I have to increase my exercise and/or lessen my food intake. I hope you can feature an article regarding this."

"Hi! I've read from a certain article that kickboxing or taebo can be harmful to the ovaries. Is this true? Are there any side effects from this workout that are dangerous for the reproductive system? I hope I'll get some information regarding this because I'm a regular exerciser who does taebo at least two times a week. A little scary for someone like me who's 24 years old and just about to get married, isn't it?"

I could not find any data whatsoever implicating taebo or kickboxing with damaging any part of the reproductive system. However, body weight and exercise can have an effect on getting pregnant. According to the American Society of Reproductive Medicine, regular exercise and a healthy diet enhance fertility by keeping body weight at normal levels and by relieving stress and anxiety.

On the other hand, excessive amounts of exercise can be a cause of infertility because it can lead to amenorrhea (absence of menstruation) in women and a lowered sperm count in men.

Body weight
It has been noted that women who are very thin and women who are obese have a difficult time conceiving. Some studies have found that 12 percent of infertility cases are due to being underweight or overweight. This is probably because body fat plays a role in reproduction. The sex hormones are "lipid soluble," meaning they dissolve in fat but not in water. Thus, they are stored in the fatty tissues of the body.

Women with very low fat levels can become estrogen deficient while women who are obese can have too much stored estrogen. Both situations can affect the normal menstrual cycle. Menstruation can become irregular or stop altogether. In some cases, even if the cycle appears normal, there is no ovulation.

Being overweight can cause insulin resistance, which increases insulin levels. This can cause the ovaries to stop releasing eggs. Exercise can help because it reduces blood sugar levels and, therefore, the pancreas doesn't need to release as much insulin.

How thin is too thin and how fat do you have to be to affect your chances of getting pregnant? Some experts say that if your weight is 85 percent lower than the normal weight range, you are too thin; if it is 120 percent higher than normal, you are too fat. However, there are some studies that show that even a slight increase in being overweight is associated with a marked increase in fertility problems.

You can find out if you are within the normal weight range by using the Body Mass Index method or BMI. To calculate your exact BMI, multiply your weight (in pounds) by 705, divide the result by your height in inches, and divide that result by your height again. A normal BMI is between 19 and 25, the overweight range is between 25 and 29, and the obese range is 30 and over.

Not all thin or obese women have a problem conceiving. Weight seems to only become a problem with regard to fertility if it disrupts the menstrual cycle. However, remember that it is possible to menstruate without ovulating so you should see a doctor if you are having a hard time getting pregnant and you are under- or overweight.

Even if being too thin or too fat does not cause fertility problems for you, both conditions are still not healthy for pregnancy.

If a woman is naturally thin because of inheriting a fast metabolism or body type (slim model-like figure called ectomorph) but she eats normally and exercises in moderation, this is not cause for concern. But if she is thin because of excessive exercise and poor eating habits, this can affect the normal growth and development of her fetus because she will tend to continue this behavior during the pregnancy.

Obese women tend to have health problems like high blood pressure, high cholesterol levels and insulin resistance. These conditions can get exacerbated during pregnancy and lead to complications that are dangerous to both the mother and the fetus.

As for men, being too thin can decrease sperm function or lower sperm count. Currently, there is not enough scientific data on how being overweight can affect a man's sperm production.

How can you tell if exercise is excessive? Just because a person works out several hours a day (like many athletes, both amateur and professional) does not automatically mean that s/he is exercising too much. People are different and what is too much exercise for one person is just a "warm-up" for another.

The best way to find out if you are doing too much exercise is to be on the lookout for the classic symptoms of overtraining.

Physical symptoms include decline in performance, inability to maintain exercise program, chronic fatigue, elevated resting heart rate, hormonal changes, slower heart rate recovery, elevated blood pressure, persistent muscle soreness, loss of appetite, unexplained loss of weight, headaches, heavy legged feeling, frequent colds and flu, gastrointestinal disturbances and menstrual irregularities.

Psychological symptoms include depression, decreased self-confidence, mood changes, apathy, lethargy, low motivation, lack of concentration, anxiety, sleep disturbance, irritability/excitability, boredom, inability to relax, anger/aggressiveness.

So if you are engaging in vigorous exercise but are not experiencing any of the symptoms mentioned above, you should be okay. Some fertility specialists, however, believe that regardless of not having overtraining symptoms, women who exercise strenuously for more than seven hours a week can experience higher rates of fertility problems.

In women, excessive exercise coupled with a very low calorie intake leads to a lowered body fat level, which in turn leads to estrogen deficiency. The result is a seemingly normal menstrual cycle without ovulation, irregular periods or no periods at all. This situation happens most often to female athletes. However, researchers have found that even if the athlete trains for many hours and has a low body fat level, if she takes in enough calories to make up for the amount of energy burned and gets enough rest, she can avoid menstrual problems. The lesson here is that you need to eat enough to fuel your strenuous workouts.

Another way that scientists believe too much exercise can affect fertility is because endorphins, feel-good chemicals similar to morphine that are released by the brain during exercise, can increase prolactin levels. Prolactin is a hormone the body uses to produce breast milk, which can interfere with ovulation (that's why many women don't become pregnant while they are breastfeeding).

In men, scientists believe that excessive exercise can reduce the sperm count for two reasons. One, strenuous exercise can cause heat to build up around the testicles. Two, too much exercise can produce high levels of adrenal hormones, which can lower testosterone.

The body keeps the testicles about half a degree cooler than core temperature because the sperm is sensitive to increased heat. Men who want to impregnate their partners should avoid anything that raises the temperature of their scrotum. This means they should avoid hot tubs, saunas, steam rooms, too tight underwear, long driving trips and hot working conditions (like working in ship's engine room).

Anabolic steroids, used by some bodybuilders to increase muscle size, can decrease sperm count as well as shrink the testicles. It is ironic, but some macho-looking men may not be so macho after all.

Damaged sperm can still fertilize an egg and this can cause birth defects, stillbirths and miscarriages. So it's important that the male partner, and not just the female, take care of their reproductive organs. Remember, it takes three months for sperm to develop. So the sperm cells you have today are a product of your lifestyle three months ago.

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