Sci. Aging Knowl. Environ., 12 February 2003
Farewell to Fatherhood
In men, sperm vitality goes the way of the hairline and the taut stomach
Key Words: azoospermia spermatogenesis sperm motility
The biological clock ticks for men, too. Sperm from oldsters loses its spunk, according to new research. The study, which bolsters the conclusions of previous, less rigorous work, suggests that would-be fathers risk infertility if they put off having children.
Although women stop making eggs after menopause, men produce flotillas of little wrigglers well into old age. The feats of some wrinkled Lotharios--such as actor Anthony Quinn, who sired two children after age 75--prove that some grandfathers are still capable of becoming fathers. However, several papers suggest that in most men, sperm mobility and amount of semen--two gauges of fertility--decline with time. Two years ago, epidemiologist Brenda Eskenazi of the University of California, Berkeley, and colleagues reviewed these studies and found methodological flaws that undercut the conclusions. Many subjects were patients at fertility clinics who probably had reproductive problems unrelated to aging. Moreover, the studies included few men over the age of 50 and often failed to eliminate factors that can harm sperm and slash semen volume, such as tobacco use and length of abstinence before providing a sample.
Eskenazi and colleagues rounded up a more representative sample by excluding smokers and men with known fertility problems. Their 97 subjects, all between the ages of 22 and 80, were current or former employees of Lawrence Livermore National Laboratory in California. In addition to supplying semen samples, the men provided data on prior incidence of sexually transmitted diseases, their history of radiation and chemical exposure, alcohol and caffeine use, time spent sitting, length of abstinence, and other potential confounding factors. After adjusting for these variables, the researchers found that age brings a gradual decline in semen volume, the percentage of sperm that move, and the percentage of sperm that squirm forward "like they've got a purpose," says Eskenazi. Compared with a 30-year-old man, a 50-year-old produces 20% less semen and 28% fewer mobile sperm. A man's fertility doesn't halt abruptly, as occurs in menopause, says Eskenazi, but the odds of conception shrivel over time. The cause of the fertility slide remains mysterious, she adds. One possibility is that whatever spurs aging also batters the reproductive system. Older men might also have incurred greater damage from environmental toxins.
"I think it's a big improvement on previous studies," says reproductive epidemiologist David Dunson of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, because it includes a range of ages and removes possible confounding variables. However, he notes that the decreases in sperm mobility and semen volume are too small to fully account for diminished male fertility. He suspects that other age-related factors are involved, such as an increase in abnormally shaped sperm or chromosome damage. The decline is particularly important today because more and more American men put off fatherhood until they are in their 40s and 50s--when they might no longer be capable. So, guys, ask not for whom the biological clock ticks. It ticks for thee.
--Mitch Leslie; suggested by Amir Sadighi Akha
February 12, 2003
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Science of Aging Knowledge Environment. ISSN 1539-6150