Women who have been forcing themselves to exercise regularly to get into shape and lose unwanted pounds may find that the benefits of their athletic pursuits extend beyond a trim look. Past research has determined that exercise may lead to a decreased chance of breast and reproductive tract cancer in women, and four Harvard researchers now hope to discover the biological basis for this reduced risk.
The group of experts last week began a three-year study, for which they received a $300,000 National Institutes of Health (NIH) grant, to closely examine the effects of exercise on "elite oarswomen," who are female athletes between 20 and 30 years of age and are competing for spots on the lightweight or heavyweight national rowing teams. The research, which should explain why only some exercising women experience the menstrual dysfunction that can lead to a reduced cancer risk, will include studies on the amount and location of fat present in the bodies of participants, as well as body fat's effect on the way estrogen is metabolized.
Athletics and Health
Rose E. Frisch, an associate professor at the School of Public Health (SPH) and principal investigator of the research team, has worked for more than a decade studying the age of menarche (the onset of menstruation) and the long-term reproductive health of former women athletes, and this work forms the basis for the current NIH study.
Frisch began the bulk of her work in the late 1970s, when she found that a group of ballet dancers she analyzed had a late menarche compared to their non-athletic peers. By 1981, Frisch broadened her study, analyzing the menstrual cycles of runners and swimmers on college varsity teams.
This later study confirmed her previous results, as she found that the selected athletes had a delayed menarche, a "lean" build and irregular menstrual cycles.
Frisch calculated that for each year of exercise, defined as two hours of energy-intensive activity twice a week, girls can delay menarche five months. A girl who begins exercising when she is nine, can delay menarche from the average age of twelve-and-one-half to the age of 15, she says.
Scientists have already associated a high risk of breast cancer with early menarche, Frisch says, so the later a girl's menarche, the better her future health will probably be. "It is a good thing for young girls to start exercise early," she says.
Frisch also concluded that some women athletes, who have lost a significant amount of body weight due to strenuous exercise, experience menstrual dysfunction and may become temporarily infertile.
"The hypothalamus normally sends out a [hormone] signal that puts the reproductive system on 'go,'" Frisch says. If body weight is too low, the brain will not send any hormonal signals to the reproductive organs, and menstruation will not occur, she says. Once exercise is cut back and weight is regained, the menstrual cycle and ovulation will be restored, and pregnancy will be possible. "The situation is not irreversible," she says.
Frisch has determined that if a woman weighs 10 to 15 percent below her normal weight, her reproductive cycle will be turned off. Doctors have even created a "fatness index," indicating the minimum amount a woman must weigh to be fertile. Women who become infertile can refer to this index to discover the weight they need to regain fertility, assuming nothing else is wrong, Frisch says.
Frisch, who works at the Center for Population Studies, conducted yet another analysis in 1985 of more than 5000 college alumnae, some of whom participated in athletics. "The alumni who had exercised in college had less cancer of the breast and reproductive system," she says.
The following year, Frisch determined further from the same data pool that the athletic women, who were between 20 and 80 years of age, had a lower lifetime occurrence of benign tumors and diabetes.
"The public health implications of those findings are a reason to find out" the biological basis of this phenomenon, says Robert Barbieri, an associate professor at the Medical School and another member of the research team.