When stories like these make headlines, people usually respond by being reminded that nature presumably favors the male sex when it comes to human reproduction. The myth goes that men can have children their entire lives. They have no "biological clocks." But after 35, a woman is considered to be "advanced maternal age." And after menopause, when a woman's ovaries stop releasing eggs, pregnancy is highly unlikely.
It's not just Hollywood men who are becoming fathers at an older age. Between 1972 and 2015, the number of men having a child over the age of 40 nearly doubled in America, according to an analysis of 168 million births. Becoming an older father is now more common, sure, but does that really mean men don't have these so-called "biological clocks" in advanced paternal age?
"As men get older, their sperm counts go down, as well as their DNA fragmentation and methylation rates go up," Dr. Aimee Eyvazzadeh, a reproductive endocrinologist based in the San Francisco Bay Area, told Salon, referring to molecular processes that can damage DNA. "And with that comes increased risks of a number of diseases that should not be taken lightly — autism, schizophrenia, ADD, ADHD, imprinting disorders."
Women have long carried the burden while trying to conceive. But as science is catching up, researchers are learning more about how age and sperm matter
Eyvazzadeh said when stories about older men in the news surface, she worries it gives the public "false reassurance" that fathering children at an old age is easy and comes without risk. Eyvazzadeh said she also suspects the public often isn't getting enough information regarding whether pregnancy was achieved. It's possible a celebrity couple did in vitro fertilization (IVF), a type of assisted reproductive technology that helps people experiencing fertility issues to conceive. These famous older dads may have frozen their sperm at a younger age, and aren't letting the public in on those details.
Nonetheless, not much has been known about the effects of advanced paternal age on pregnancy and their offspring until relatively recently. Instead, overwhelming focus has been put on the maternal age and the effect it has on fertility and pregnancy outcomes. As a result, women have long carried the burden while trying to conceive. When unable, the blame was more often cast on the female sex — not male. But as science is catching up, researchers are learning more about how age and sperm matter. In December 2022, a review of existing studies concluded that being an older father "is associated with reduced fertility and poor health effects in offspring."
In one study, researchers found that sperm motility, which is the ability of sperm to move efficiently, and the percentage of "normal sperm" declined slowly starting at 30 years of age compared to sperm of 20 to 29-year-olds, suggesting that it could take couples with older fathers longer to get pregnant. According to data published by researchers at Stanford University, babies born to fathers over the age of 35 also had a higher risk for adverse birth outcomes. For men who were over the age of 45, they were 14 percent more likely to have a baby born prematurely and 28 percent more likely to have a baby that needed to go to a neonatal intensive care unit after birth.
"While the oldest father ever is reportedly 96 and biological potential does persist, a man's fertility does decline with age," Dr. Michael Eisenberg, a professor of urology at Stanford University School of Medicine and one of the researchers of the aforementioned study, told Salon via email. "Data suggests that semen quality drops with age and it takes men longer to conceive as they get older."
Eisenberg said he thinks more education is necessary to let men and couples know changes that accompany decline in male fertility with age.
"Studies have shown that the risk of several conditions do increase as men age; there are rare conditions due to mutations such as achondroplasia, [a condition which presents as dwarfism], which increase in risk as men age," he said. "Neurodevelopmental outcomes are also associated with increasing paternal age."
Eisenberg added that research has suggested that there is a higher risk of cancer in children with older fathers. In 2015, a study published by the American Cancer Society found a link between a baby's risk of blood cancer as an adult and the father's age. Specifically, babies whose fathers were over the age 35 at birth had a 63 percent higher risk of hematologic malignancies when compared to those whose fathers were under the age of 25.
"However, it's important to know that most of these conditions are rare," Eisenberg said. "While the relative risk does increase, the absolute risk remains low."
Eyvazzadeh said the increase in research around how male sperm can be affected by age is certainly contributing to a paradigm shift in how the medical world views and understands fertility.
"I think there are more studies coming out that are published and well done, showing how important sperm quality is, and I think fertility doctors are definitely understanding that," Eyvazzadeh said. "Fifteen years ago, no one was listening, no one was talking about it, they would say, 'Oh, you just need sperm, it doesn't matter the quality,' and now we're understanding more about epigenetics and how important sperm quality is. You're not just what you eat — you are what your dad ate as well."
This paradigm shift is also happening at a moment when male fertility is declining. Over the past 50 years, sperm counts appeared to decline by more than 50 percent worldwide. As far as a "cut off" age for when risk rises, or when a man is considered to be "advanced paternal age," it depends on who you ask. Eyvazzadeh said in her opinion it's 50, although some people say 40.
"When I have a patient that's over the age of 50, I ask them to do more advanced sperm tests, like the DNA fragmentation or DNA methylation tests, in addition to semen analysis," Eyvazzadeh said. "And then I make sure they're on a lot of supplements, so that their sperm is as healthy as possible, and I talk to them about the risks associated with age over 50."
