It's a well-known fact: Men don't go through menopause. They are generally capable of procreation into old age. But time still leaves its mark.
The older men get, the higher the risk of their newborn children inheriting mutations via their sperm, said Christian Leiber-Caspers. "In a number of studies, it has been found that men who are over 40, over 50 or over 60 have such changes."
Leiber-Caspers is head of andrology at the Clinic for Urology, Pediatric Urology, Urogynecology and Andrology at the Maria-Hilf Hospital Alexianer Krefeld in Germany. Andrology is an area of medicine that's specifically concerned with men's health.
"Statistically, the risk of birth defects is greater," said Leiber-Caspers.
The number of mutations in a man's sperm increases with each passing year.
When new sperm are created, their complete genetic material is duplicated from existing sperm cells. This process of repetitive copying can lead to the risk of minor or major errors over time. These errors can then multiply over the years.
In addition, the body becomes less able to automatically repair possible defects in the genetic material as men get older.
If a man in his 20s passes on about 20 mutations to his child, a man in his 40s may pass on 65 such mutations. The child of an older man will then pass on a large number of new mutations to his own child or children, who in turn will pass them on to their children.
Constant stream of sperm
Women have a limited number of eggs, and these begin to dwindle from the day they are born. Menopause begins around the time that most of the eggs have been expended.
A man, on the other hand, constantly produces new sperm.
"In a healthy young man, we assume he has more than 39 million sperm in one ejaculate sample. Some may even have as many as 200, 300 or even 400 million sperm," Leiber-Caspers said. "Although you send quite a few million sperm to the starting line, in the end it is only a single sperm that fertilizes the egg."
So, it's an intensive and competitive selection process. Only the most mobile sperm have a chance of getting to and entering the egg cell.
But even if about 90% of the sperm fail, and some carry defects, that is perfectly okay from a biological point of view, said Leiber-Caspers.
New parents are increasingly older
The average age of first-time mothers in Germany has continued to rise in recent years, reaching 30.5 years in 2021, according to the German Federal Statistical Office.
For a woman over 35, pregnancy is considered a high-risk pregnancy. The child may, for example, develop trisomy 21, also known as Down syndrome.
First-time fathers in Germany are also getting older, with an average age of 33.3.
In the past 10 years, researchers have looked at the male biological clock and the risks in late fatherhood. But this has not yet led to clear results or recommendations.
Conducting such studies is complicated because researchers say a mother's data must also be taken into account and that that introduces unlimited variables.
"It is difficult to see what exactly are the individual factors that can then be decisive for the health of the child," explained Leiber-Caspers. "However, there are certain conditions where you are relatively certain that the father's older age plays a role."
Fatherhood in older age increases the risk of hereditary disease
Researchers have identified about 20 hereditary diseases that are associated with a father's age. While trisomy 21 is mainly associated with a mother's physiology, a father's age can also play a role in a child's mental or psychological health, including the development of schizophrenia or bipolar disorder.
Children who were born when their fathers were over the age 45 years have a 3.5 times higher risk of developing autism than children who were born when their father was in his early 20s, researchers have found.
Hereditary diseases include antiphospholipid syndrome (APS), an autoimmune disease. It can manifest itself in pulmonary embolisms, arthritis or memory disorders and epilepsy.
The prevalence of attention deficit disorder (ADHD) was about 13 times higher in children who had older fathers, and the prevalence of bipolar disorder was about 25 times higher, according to studies.
All of this, however, is a "possibly could happen" but not a "definitely will happen."
Older fathers also have advantages
On the social and societal level, older men have some advantages as well. They are often professionally stable, economically secure and have a solid social network. If they are at a very advanced age, they can devote more time to their children than perhaps younger men who are just starting to establish themselves in life.
And even if the sperm of a 40, 50, or 60-year-old man is no longer quite as mobile as that of a younger man, a father older than 35 may be a little more relaxed and also a little more generous in his interactions with his children.
"A calendar 60-year-old may only be biologically 50 or 55, but of course you can debate whether someone in his 70s can still fulfill his role as a father and really keep up with his children in the same way as a man in his 20s or 30s," said Leiber-Casters.
This article was translated from German.