Study Shows His 'Biological Clock'
Is Ticking Too

NEW YORK (Reuters Health) - While much has been made of women's "biological clocks," new research confirms that men have them too--although the male clock is slower to wind down.

According to researchers, the findings show that a caution often directed at women may apply to men as well: Waiting till middle age to try to have kids may dampen the odds of success.

The small study suggests that as healthy men age, their sperm begin to slow down and lose sight of their goal--swimming in circles rather than sprinting for the female egg.

The scientific term for speedy, goal-oriented sperm movement is "progressive motility." And among the 97 study participants, progressive motility declined 3.1% each year.

Overall, the number of men with abnormal sperm concentrations or movement increased with each decade of age, according to findings published Thursday in the journal Human Reproduction.

"Because semen quality is a proxy for fertility, these data suggest that men may become progressively less fertile as they age," write the authors, led by Brenda Eskenazi of the University of California, Berkeley.

For women, fertility is known to markedly decline around the mid-30s. The new findings indicate that a 30-year-old man has about a 50% chance of having abnormal progressive motility--odds that increase to 67% by age 50 and 84% by age 80.

"Women tend to be the focus in fertility issues," Eskenazi said in a statement. "What we are saying is that men are not scot-free in this."

She added that, although everyone has heard of men fathering children in their 70s and beyond, the true odds of success "may be lower than we thought."

The study included 97 volunteers ages 22 to 80 who were all employees or retirees from the Lawrence Livermore National Laboratory. The men provided semen samples and details about their lifestyle habits, medical conditions and occupational exposures.

All of the men were non-smokers, and there was no evidence that occupational exposures at the government research facility explained the age-related decline in semen quality, according to the researchers.

They speculate that certain physiological changes that come with aging--such as narrowing of the testicular tube or normal changes in the prostate--may explain their findings.

Another possibility, they add, is that older men, by virtue of their longer lives, were more likely to have been exposed to tobacco smoke or some other environmental toxin that may harm semen quality.

SOURCE: Human Reproduction 2003;18:447-454.

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