SAN FRANCISCO--Men have biological clocks that cause their ability to father healthy children to ebb with time, according to study findings released on Monday by US researchers.

DNA in sperm fragments as men age, increasing the risk of infertility or of babies being born with anomalies such as dwarfism, scientists at the University of California, Berkeley, and Lawrence Livermore National Laboratory concluded.

"We know that women have a biological time clock," said study co-author Brenda Eskenazi of the university's School of Public Health.

"Our research suggests that men, too, have a biological time clock, only it is different. Men seem to have a gradual rather than an abrupt change in fertility and in the potential ability to produce viable healthy offspring."

Earlier research by the same team indicated that sperm counts decline and sperm loses its ability to move spontaneously and in straight lines as men age.

The current study, which will be featured this week in an online edition of Proceedings of the National Academy of Sciences, focused on genetic damage or mutations in semen from men of varying ages.

"This study shows that men who wait until they’re older to have children are not only risking difficulties conceiving, they could also be increasing the risk of having children with genetic problems," said co-author Andrew Wyrobek of the national lab.

The 97 men that took part in the study were healthy, non-smoking, lab employees or retirees ranging in age from 22 to 80 years old, according to authors.

A supplemental study involving men from the US city of Baltimore indicated that dietary, ethnic, or socio-economic background could exacerbate the effect age has on sperm quality.

Understanding ramifications of paternal age has become increasingly important because of a trend for US men to become fathers later in life, according to the study's authors.

The number of men ages 35 to 49 fathering children has risen approximately 40 percent since 1980, while there has been a 20 percent drop in the number of fathers younger than 30, statistics cited by researchers indicated.

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hahaha... well said tokayo....

i hav a 3 yr old daughter... i dont know about my tokayo...

hahaha u'v got an understanding wife? or sawa na sya sa yo at parang pinamimigay/pinahihiram ka na?

well, it's really very hard having more children... maliban sa puyatan pg maliit pa, pwera p dun pg ngkasakit.... and the cost of living... tsk tsk tsk