Do men have a biological clock? Experts say it’s not just women who need to worry about age and fertility.

When it comes to childbearing, the focus often falls on women and their (ticking) biological clocks. However, it’s not just women who need to consider their age when thinking about when to have children. Experts agree that the fertility of men also depends on their age.

According to reproductive endocrinologist Jane L. Frederick, PhD, women receive the most attention because they are born with a limited number of eggs and must deal with changes in egg quantity and quality beginning at age 35.

“Women play a distinct role in reproduction, which leads us to believe that topics such as fertility, pregnancy and childbirth are women’s issues and that men are no longer involved after providing sperm,” she explains. “However, older men over the age of 45 are more likely to have children than they were forty years ago, but few realize that their biological clocks are ticking as well.”

A 2017 study of IVF patients conducted by Beth Israel Deaconess Medical Center and Harvard Medical School found that while women between the ages of 40 and 42 had the most difficult time conceiving, older men were less likely to have a live birth – even if those partners were younger women. Exactly why this is the case, however, remains to be studied.

Dr. T. Mike Hsieh, director of the UC San Diego Men’s Health Center and professor of urology, told Yahoo Life that while the “data” on male fertility is not as good as for women, it is clear that “increasing paternal age is associated with decreased fertility “in terms of sperm count, sperm quality, semen volume, testosterone and sexual mobility or erectile dysfunction.” Although there is no “specific cutoff,” the general consensus is that advanced paternal age begins at about age 45.

Dr. Paul Turek, a urologist and male fertility specialist, added that men in their 50s and 60s have a “significant decline” in fertility compared to younger men. The reason for this decline, he says, may be not only the body’s biological clock, but also certain risk factors that rise as men get older. As he points out, “the body has to be very healthy to reproduce properly.” He added that as men age, “the quality of the DNA package” can “change or decrease.

“This means that when the DNA payload is passed into the egg at fertilization, it is broken down into single strands rather than complete double strands,” Turek explains. “The egg does what it can to ‘repair’ the DNA early after fertilization, but if the damage load exceeds the egg’s ability to repair it, then there is no pregnancy or possible miscarriage – another situation where, on a biological level, the women clean up what men make.”

Frederick also noted that “as men age, the risk of developing diseases or being exposed to environmental toxins increases,” which may reduce their fertility.

“A history of chronic medical conditions, such as sickle cell disease, chronic renal failure, cirrhosis or liver diseases such as malnutrition, may affect sperm production,” she noted. “Men who develop health problems later in life may be taking medications that can adversely affect sperm function.”

Over time, men’s testosterone levels steadily decline, which can also affect their ability to produce children.

“Declining testosterone levels in men can lead to decreased libido, erection problems and ejaculation difficulties – all of which can lead to infertility in couples,” Frederick explained. “Testosterone levels do seem to affect sexual function and libido. In men, testosterone replacement therapy can improve erectile function, but it can also lead to decreased sperm production and cause infertility.”

Ultimately, however, Frederick notes that the field still has a long way to go. “Many unknowns remain about older men and infertility,” she said. “Further research will allow us to better understand age and its impact on all areas of male infertility.”