It has long been known that females have a ticking biological clock when it comes to reproduction, but evidence suggests that male fertility also declines with age. This is a particularly important finding given that many men are now fathering children when they are older. Though perhaps not as dramatic as the impacts of mothering at an advanced age, the age-related decline in male fertility is nonetheless an important issue that men wanting to have children should consider when family-planning.
Part of male age-related fertility problems has to do with the quantity and quality of sperm that a man can generate. As a man ages, he produces declining volumes of semen. One study found this reduction to be 3 and 22 percent less volume at age 50 than at age 30. In that same age range, the concentration of sperm within semen also decreases to as much as 37 percent. In addition to that, the motility of sperm decreases 4 to 18 percent. This can greatly increase the difficulty involved with trying to conceive a child.
In addition to problems with conceiving, men that wait to father children may also put their children at a greater risk for genetic defects. As men age, their cells are likely to accumulate DNA damage due to single nucleotide polymorphisms and other mutation events. In most of the body’s cells, this damage will have not affect fertility. However, if the cells involved with spermatogenesis acquire these mutations, they will impact all the subsequent sperm cells produced. Studies have shown that with each passing year men have the potential to pass on two new mutations to their offspring. This evidence led researchers to suggest that men may pass on a higher number of mutations to their children than women.
In addition, an increased paternal age has also been correlated with an increased chance of offspring developing neurocognitive disorders such as schizophrenia and autism. One study found that men over age 40 were 5.75 times more likely to have children on the autism spectrum than men under age 30. Another investigation found that fathers over age 45 were twice as likely than fathers in their twenties to have children suffering from schizophrenia. Other disorders such as childhood cancers, leukemia, bipolar disorder, and a variety of congenital disorders have also been linked to increased paternal age. While these are only correlations, the evidence supports the previously discussed hypothesis that older men have more genetic defects in their sperm, and thus would be more likely to have children with genetically-influenced diseases.
However, unlike with female fertility, there does not seem to be a clear cut-off age at which fertility declines and the risks conferred to a child increase. In general it is hard to study the effects of aging on male fertility because of many confounding factors such as the age of the mother, genetic predisposition, and environment can influence reported results.
The information that male fertility declines with age is particularly important for men both young and old. Younger men looking into family planning might consider not waiting too long before having children. In the future, older potential fathers may choose to be evaluated for their risk of conferring potential genetic disorders to their offspring. However in the mean time more research is required to understand this complex issue.
By Sarah Takushi