US scientists conducted a study of sperm from around 100 healthy, non-smoking men aged 22 to 80 and found a prevalence of certain genetic damage increasing with age. This in turn can be manifested as symptoms such as infertility, difficulty in their partners becoming pregnant miscarriages and an increased risk of the offspring inheriting genetic diseases such as dwarfism.
'There is consequence to delaying fatherhood,' said Andrew Wyrobek, lead researcher of the study and a biophysicist at the Lawrence Livermore National Laboratory in California. 'The probability of infertility goes up, the risk of abnormal pregnancy goes up and the risk of dwarfism goes up, and perhaps other genetic diseases as well.'
The study revealed that with increased age there appeared to be increased DNA breakage in sperm, increased conditions that lead to infertility or miscarriages. In addition it was found that gene mutation causing dwarfism were also increased.
According to the researchers compared with men in their 20s, a 50-year-old has a 34 per cent higher risk of producing a child who is a dwarf, while an 80-year-old's risk is 85 per cent higher.
However, chromosome number related diseases like Down syndrome, Turner syndrome and triple X syndrome appeared to be unaffected by male age.
'We know that women have a biological time clock with an increase in risk of miscarriage and producing children with trisomy (an extra chromosome) as women age, and with a seemingly abrupt end of fertility around perimenopause,' said co-lead author Dr. Brenda Eskenazi of the School of Public Health at the University of California, Berkeley.
'Our research suggests that men, too, have a biological time clock - only it is different,' Eskenazi said in a statement. 'Men seem to have a gradual rather than an abrupt change in fertility and in the potential ability to produce viable healthy offspring.'
The study of paternal age is important considering the fact that paternal age has been rising steadily over the past few decades. Since 1980, there has been about a 40 per cent increase in 35-to 49-year-old men fathering children, and a 20 per cent decrease in fathers under 30. Studies have also shown that it takes longer for older men to conceive, even when the age of the mother is considered.
Commenting on the size of the study, Toronto urologist Dr. Kirk Lo said that with fewer than 100 subjects covering such a wide age range, the findings were open to interpretation.
'In older men, they may have increased sperm DNA fragmentation and that could affect fertility,' he said. 'But is this due to environmental factors or is it intrinsic to aging? It's difficult to say.'
The results of the study have been published in the online edition of the Proceedings of the National Academy of Sciences.