The concept of the female biological clock is no secret. Seemingly everyone knows—and likes to remind women of a certain age (trust me) that the bell starts to toll towards the mid-thirties, gets louder and more urgent in the late thirties and early forties, and falls completely silent at menopause, around age 50. The male biological clock, on the other hand, is rarely mentioned, and why should it be? After all, Al Pacino had a baby at 83, Robert De Niro at 79, Mick Jagger at 73. It’s easy to wonder: is there even such a thing as the male biological clock?
The short answer is yes, but it doesn’t look anything like the fairer sex’s. “The big difference is that on the female side, a woman is born with all the eggs she’ll ever have throughout her life. And on the male side, there is this constant turnover production of sperm, because the testicular tissue is making sperm each and every day,” says Brent Hanson, MD, a fertility doctor at CCRM Fertility. While women eventually reach the end of their finite egg supply, men continue this daily sperm production throughout life. “You can see a 90-year-old guy in a wheelchair rolling down the hall, and he’s making fresh new sperm every day,” says Kian Asanad, MD, incoming Assistant Urology Professor at the USC Keck School of Medicine.
This doesn’t mean, however, that the sperm of a 90-year-old man is just as healthy as the sperm of a 25-year-old man, or that older men won’t have more trouble achieving a healthy pregnancy or producing healthy offspring than younger men. “Aging still has significant implications in terms of male reproductive and sexual health,” says Dr. Asanad.
The Effects of Aging on Male Fertility
To begin with, the sperm of an older man does not look the same under a microscope as that of a younger man. “Semen analyses show significant changes over time as men age,” says Dr. Hanson. According to a meta-analysis referenced by Dr. Asanad, sperm volume decreases by 3-22%, sperm motility (the ability of the sperm to move) worsens by 3-37%, and rates of abnormal morphology (the size and shape of the sperm) increase by 4-18% as men age. These declines are mirrored by changes “on the molecular, genetic level—we can see higher rates of damaged DNA inside individual sperm cells as men get older,” says Dr. Hanson.
These changes impact fertility in a number of ways. A decrease in semen volume can lead to a decrease in sperm count, resulting in lowered odds of conception. Worsened sperm motility likewise reduces the odds of conception, as it means sperm are swimming less efficiently through the female reproductive tract—they may be swimming more slowly, in circles, or not moving forward at all. And increased rates of abnormal morphology mean there will be more abnormally shaped sperm approaching the egg, and those sperm tend to have difficulty penetrating the egg in order to fertilize it. Sperm DNA damage above a certain threshold, meanwhile, is associated with recurrent miscarriage, recurrent IVF failure, and poor fertilization of eggs.
Beyond these changes in sperm quality, the other relevant shift men experience as they age is in testosterone levels, which are a critical component of fertility. “Endogenous testosterone production, meaning from within a man’s own body from within their testicles, plays a huge role in sperm production,” says Dr. Asanad, who adds that it can additionally impact sperm quality and function beyond sperm count. “Men with low testosterone also have decreased libido, decreased frequency of intercourse, and they may have erectile dysfunction—all of which play a role in fertility,” says Dr. Asanad.
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