Too much exercise can reduce a woman's fertility

Women who exercise intensively on a daily basis are three times more likely to have fertility problems, according to a new study.

But the good news is that the effect does not seem to be long-lasting.

In the study, which was conducted at the Norwegian University of Science and Technology, fertility problems were defined as not conceiving within a year of trying, even if the woman subsequently falls pregnant. In Norway this applies to around 7% of the population as a whole.

Over 3,000 women were surveyed for the study, all of whom were healthy, of childbearing age and without a history of fertility problems. The women's lifestyles were examined in 1984-86 and again in 1995-97.

In the first occasion they were asked about frequency, duration and intensity of their physical activity - and ten years later were asked questions about pregnancy and childbirth.

"Among all these women, we found two groups who experienced an increased risk of infertility" said researcher Sigridur Lara Gudmundsdottir. "There were those who trained almost every day. And there were those who trained until they were completely exhausted. Those who did both had the highest risk of infertility."

This effect was even more marked if the woman was under the age of 30.

Among those who reported training to exhaustion (regardless of how often and for how long), 24% had fertility problems. In the group that had trained almost every day (regardless of the intensity and duration), 11% reported the same.

Even when the data were adjusted for other possible contributing factors (such as body mass index, smoking, age, marital status and previous pregnancies), researchers found that women who trained every day had a 3.5 times greater risk of reduced fertility as women who didn't train at all.

"And when we compared those who trained to exhaustion to those who trained more moderately, we found that the first group had a three-fold greater risk of impaired fertility" said Ms Gudmundsdottir.

Effect not permanent

"The vast majority of women in the study had children in the end. And those who trained the hardest in the middle of the 1980s were actually among those who had the most children in the 1990s," explained Ms Gudmundsdottir.

It has been suggested that the body is unable to cope with the demands of intensive exercise and becoming pregnant at the same time - there simply is not enough energy to maintain all the necessary hormonal mechanisms that enable fertilization.

But it should be noted that some exercise is actually beneficial to a woman's chances of getting pregnant.

"We believe it is likely that physical activity at a very high or very low level has a negative effect on fertility, while moderate activity is beneficial" she says.

This article was published on Mon 9 November 2009