File photo: Only four percent of children were born to fathers aged over 45 in modern Sweden. Picture: ANA Pictures

London - Older fathers are more likely to have children who are less fertile, a major study has found.

Researchers found that their offspring typically go on to have fewer children of their own.

The effect was not found in those with older mothers when the family records of 1.4 million people were examined.

The academics believe that as a man ages, more mutations occur in his sperm which affect a child’s fertility later.

Sperm production goes on throughout life but as the cells which create it divide, more errors gradually creep into the DNA.

In contrast, women are born with all the eggs they will ever have. 

Most of the DNA changes have no effect but some may affect the ability of a man’s children to reproduce.

On average, a person will have around 60 such mutations which are not present in either parent. The researchers led by a team at Georg August University in Gottingen, Germany, were testing the theory that the father’s parental age was linked to reduced fertility and survival in his offspring.

By looking at computerised family records in Sweden, Canada and Germany, they tracked the age of children’s fathers at the time of their birth.

They then looked to see if the offspring survived to reproduce themselves and how many children, if any, they had.

Three of the populations were pre-industrial (living between 1670-1850) to rule out any effects being caused by a modern feature like plastics or chemicals.

The fourth population covered modern Swedes born after 1932. The study found that the children of older fathers were less fertile in all age groups.

But they also found the children of older fathers were less likely to survive childhood in the pre-industrial period. This effect was only found to a "minuscule" extent in the modern sample, said the authors in the journal Proceedings of the Royal Society B: Biological Sciences.

They did not define an "older father" but looked at the effect each additional year of a man’s age had on his child’s fertility.

The report said that, contrary to popular belief, the average age of modern fathers was not older but younger.

Only four percent of children were born to fathers aged over 45 in modern Sweden.

The study added that the average age of becoming a dad in modern Swedish society was around 32 compared to 36 between 1760 and 1850.