Do men have biological clocks? It's not just women who have to worry about age and fertility, experts say.

When it comes to fertility, the focus tends to fall on women and their (loudly ticking) biological clocks. Yet it’s not just women who have to take age into account when considering when to have children. Experts agree that men's fertility also depends on their age.

According to Dr. Jane L. Frederick, a reproductive endocrinologist, women get most of the attention because they have a finite number of eggs at birth and must contend with changes in egg quantity and quality starting at age 35.

“Women play an obvious role in reproduction, leading us to believe that the topics of fertility, pregnancy and childbirth are women’s issues, void of male involvement after they provided sperm,” she explains. “However, older men over the age of 45 are much more likely to have children than four decades ago, and yet few men recognize their biological clock is ticking as well.”

A 2017 study from Beth Israel Deaconess Medical Center and Harvard Medical School looked into IVF patients and found that while women of age 40 to 42 had the most difficult time conceiving, the chance of a live birth decreased with older men — even those whose parters were younger women. Exactly why that is, however, remains to be researched.

Dr. T. Mike Hsieh, the director of UCSD Men’s Health Center and professor of urology, tells Yahoo Life that although there is “not as much data” on male fertility as for females, it’s clear that “increased paternal age is associated with decline in sperm count, sperm quality, semen volume, testosterone and ability for sexual activity or erectile dysfunction.” While there isn’t a “specific cutoff,” what's generally accepted as advanced paternal age starts at around 45.

Dr. Paul Turek, a urologist and expert on fertility in men, adds that men in their late 50s and 60s experience a “definite decline” in fertility compared with younger men. The cause of this decline, he says, may not only be a body’s biological clock, but also the fact that certain risk factors go up as men age. As he notes, “a body has to be very healthy to be normally fertile.” He adds that the “quality of the DNA package” is “altered or reduced” as men age.

"That means that when the DNA payload gets delivered to the egg at the time of fertilization, it is broken into single strands, rather than intact, in double strands,” Turek explains. “Eggs try as hard as they can to ‘fix’ the DNA early on after fertilization, but if the load of damage is in excess of the egg’s capacity to repair it, then there will be no pregnancy or possibly a miscarriage — another case, at a biological level, of women cleaning up the messes that men make.”

Frederick also points out that “the risk of developing a medical condition or being exposed to environmental toxins increases with age for men,” which may make them less fertile.

“A history of chronic illness, such as sickle cell disease, chronic kidney failure, liver conditions like cirrhosis or malnutrition may have an effect on sperm production,” she notes. “Men who develop medical problems later in life may be taking medications that can affect sperm function in an adverse way.”

Men’s testosterone levels steadily decline over time, which can also affect their ability to father a child.

"Declining testosterone levels in men may cause a decline in sexual desire, problems with erection and difficulty in achieving ejaculation — all contributing to the couple’s infertility,” Frederick explains. “The level of testosterone does appear to influence the sexual function and desire in a man, and testosterone replacement improves erectile function, but also causes sperm production to go down and lead to infertility.”

Ultimately, however, Frederick notes that this field has a long way to go. “Many unknowns remain with regards to the older male and infertility,” she says. “Further research will give us a better understanding of age and its impact on all areas of male infertility.”

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