Like moms, American dads are getting older, according to a new study. Unfortunately, there is no data to suggest that their jokes are getting funnier.
Between 1972 and 2015, the median age of fathers in the US increased by 3.5 years, from 27.4 to 30.9 years. The percentage of fathers in their forties has more than doubled, from 4.1 to 8.9 percent. Similarly, fathers age 50 and older jumped from 0.5 to 0.9 percent. And the increase in graying pops occurred across races, education levels, and regions.
The study, led by Stanford researchers and published this week in Human reproduction, provides the most comprehensive look at paternal data to date, collecting paternal data from nearly 169 million birth records over the four decades. And the researcher’s finding of aging dads across the board is a mixed bag, they write.
As men age, sperm quality declines. Researchers estimate that the germline — the cellular lineage of sperm — picks up two mutations per year. Many studies have linked older fathers to an increased risk of “autism, psychiatric disorders, neurological disorders such as neurofibromatosis, childhood cancer and chromosomal abnormalities” in children.
That said, older dads seem to be better fathers than their younger counterparts, according to previous research. Fathers aged 35 to 44 are more likely to live with their children, suggesting they are there and more involved with their offspring. And having a father at birth leads to better child health and lower infant mortality.
The data doesn’t explain exactly why fathers age, but the same trend has been seen in mothers and in other countries. Between 1970 and 2000, the median age of American mothers increased by 2.6 years, from 24.6 to 27.2. And the average age of mothers at the birth of their first child increased by 4.9 years between 1970 and 2014, from 21.4 to 26.3. (The current study didn’t look at the age of the first father, but previous work has suggested that it is also increasing. It jumped from 25.3 in 1988 to 27.4 in 2010. And American families are now having fewer children on average than in the 70s).
Researchers attribute the jumps in parental age to women having greater access to the workforce and higher education, plus improved birth control and fertility treatments.
While every demographic assessed in the new study showed an upward trend in father age, the oldest fathers were Japanese, with an average of 36. White and black fathers were the youngest. The following also applies: the lower the level of education, the lower the average age of the father. Fathers with a college education had an average age of 33.3 years. Northeastern and Western regions had the highest mean paternal age.
The study has limitations, the authors note. To begin with, the data set was incomplete because some data points were missing for certain time periods and demographics. To make up for that, the researchers had to turn to modeling. But even when they entered the lowest age recorded in the data (11) to replace all the missing data, they still saw upward trends.
Overall, the researchers conclude:
Our findings support the need for further research into the health and social implications of older fathers, as fathers’ ages are indeed rising in the US.
Human reproduction2017. DOI: 10.1093/humrep/dex267 (About DOIs).