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Babies or barbells: make your choice.

Babies or barbells: Make your choice

Strenuous exercise, especially when accompanied by unusual diets or substantial weight loss, has been known to upset hormonal control of reproduction in humans. Recent research is helping to explain the nature of these troublesome imbalances, which can delay the onset of menstruation, and is suggesting a few possible benefits as well.

David C. Cumming of the University of Alberta in Edmonton reports that exercise can change the pattern of hormonal pulses that normally initiates a menstrual cycle. Normally, gonadotropin-releasing hormone is released from the brain in pulses every 90 to 120 minutes, causing a similarly pulsed release of luteinizing hormone (LH) from the pituitary. The frequency and amplitude of these pulses are decreased in some women athletes, especially after exercise, causing amenorrhea or lack of menstrual periods. Moreover, many women athletes who do menstruate nevertheless fail to ovulate and so cannot become pregnant.

Although exercise-induced amenorrhea is usually reversible, other medical consequences of these changes may be more significant, Cumming says. For example, emenorrheic women tend to gradually lose bone mass. Cumming says amenorrheics in their 20s and 30s, who should be building up to their peak bone mass, may be at greater risk for osteoporosis, a degenerative bone disease, later in life.

But according to Rose E. Frisch of the Harvard School of Public Health in Boston, exercise-induced suppression of the reproductive system may have benefits, too. Studies by iFrisch and her colleagues show that women who were athletes in college have half the rate of breast cancer and less than half the rate of reproductive system cancers compared with women who were not athletes. Lower hormone levels have in the past been associated with lower rates of cancer, and Frisch hypothesizes that the latest observations can be explained by the lower estrogen levels found in women who exercise more.

In the distant past, she says, such a mechanism might have had survival advantages by preventing pregnancy during strenuous times, such as when a tribe was moving to a new area. She suggests that the relative lack of exercise in modern life may be contributing to a gradual trend toward earlier onset of menstruation. Girls today begin menstruating three years younger than their counterparts did 100 years ago.
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Title Annotation:strenuous exercise may upset hormonal control of reproduction in women
Publication:Science News
Date:Feb 27, 1988
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