A new study, published in the Proceedings of the National Academy of Sciences, has found that sperm quality may deteriorate as men age. The study, which involves a relatively small number of volunteer subjects, was conducted at the Lawrence Livermore National Laboratory in California. Ninety-seven healthy, non-smoking men were recruited from the current workforce at the laboratory and those that had retired, with an age range of 22 to 80. Those enrolled into the study were approximately evenly divided by decade so changes in sperm genetic quality could be compared over time.
Sperm samples were collected from the volunteers over a two-month period and were required to be delivered to the laboratory within two hours of ejaculation. The samples were then examined using a technique called flow cytometry. This approach allowed the researchers to study the quality of sperm DNA, in addition to the usual male fertility indicators of sperm quantity, shape and motility. The team found that sperm numbers and motility were unchanged across the group, but they did detect changes in DNA quality that could indicate a possible deterioration linked to increasing age. Unlike eggs, which are produced before birth and age with the woman, sperm are continuously produced from sexual maturity through to old age. This had been thought to protect men from the kind of risks associated with older mothers.
In this study the researchers show that while men do not seem to have an increased risk of Down syndrome, commonly associated with older mothers, there may be greater risk of passing on other genetic disorders. As the men aged, the team found that the number of genetic mutations that can lead to achondroplasia (a common form of dwarfism) increased at a rate of about two per cent per year. Compared to the younger men, the oldest volunteers had five times as many sperm showing some DNA fragmentation, which can be associated with both genetic anomalies in the offspring and infertility. Although the general trend toward increasing deterioration with age was clear, there were disparities in each age group, with some men in the oldest bracket showing few mutations and some in the lower cohorts with many.
Brenda Eskenazi, an epidemiologist at Berkeley University and co-lead investigator of the study commented, 'We know that women have a biological time clock. 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 to produce viable healthy offspring'. She added, 'Men need to consider not just the female's fertility, but their own, and not just their fertility but their ability to produce healthy offspring'.