Researchers from Australia looking at data on US families found that young children of older fathers performed less well in a range of cognitive intelligence tests up to the age of 7 years, but were unable to say whether those children were able to catch up when they got older.
The study was the work of Sukanta Saha from the Queensland Centre for Mental Health Research, The Park Centre for Mental Health, Richlands, Australia, and colleagues from other research centres in Australia, and was published online in the open access journal PLoS Medicine.
There is good evidence that specific disorders are linked with older fathers, but the link between children’s general intelligence and fathers’ age is not very clear, said an editorial comment accompanying the article.
One study has shown a link between lower intelligence and very young and older fathers, so the authors wanted to look at the issue more closely and see if there was a link between age of fathers and children’s ability on intelligence tests. They also wanted to see if there was evidence to support another finding that older mothers tend to have more intelligent children.
For the study the researchers looked at records from the US Collaborative Perinatal Project, and analyzed data on 33,437 children who had undergone tests of cognitive ability at 8 months, 4 years and 7 years.
The tests measured children’s ability to think and reason, assessing things like concentration, memory, learning, understanding, speaking, and reading. Some tests also assessed physical co-ordination or “motor skills”.
The tests included the Wechsler Intelligence Scale for Children, Bayley scales, the Stanford Binet Intelligence Scale, the Graham-Ernhart Block Sort Test, and the Wide Range Achievement Test.
Saha and colleagues analyzed the data using two models. In the first model they took into account physical factors such as the age of the parents. In the second model they added social factors such as parents’ education and income, both factors that are known to affect intelligence. The researchers also grouped the children according to maternal age, and within each group looked for links between the lowest scores and paternal age.
They found that the older the father, the poorer the results (the exception was the Bayley Motor score), but there was no such link with the age of the mother; in fact maternal age was “was generally associated with better scores on these same measures”, they wrote.
Saha and colleagues also wrote that the “findings were broadly consistent in direction and effect size at all three ages”.
They concluded:
“The offspring of older fathers show subtle impairments on tests of neurocognitive ability during infancy and childhood.”
“In light of secular trends related to delayed fatherhood, the clinical implications and the mechanisms underlying these findings warrant closer scrutiny,” they added.
The sudy is the first to show that older fatherhood gives rise to children that perform less well on intelligence tests when young, but it can’t say whether these children catch up with their peers after the age of 7.
The editorial comment also cautioned that the results could be biased because some of the records did not have any information on the father’s age.
The last few decades have seen an increasing trend in the developing world toward couples waiting until their late thirties to have children. And while we have known for some time that older mothers are more likely to give birth to children with disabilities like Down’s syndrome, it wasn’t until recently that we discovered older fatherhood might also bring risks.
We now know that older fatherhood is linked to miscarriages, birth deformities, cancer, and brain development disorders such as autism and schizophrenia, as well as dyslexia and reduced intelligence.
Rates of autism have gone up in recent decades, but nobody knows why; some suspect it is genetic, others that it could be damage to sperm, which increases as a man gets older. While women’s eggs are formed in the female fetus before she is born and stay like that until they are fertilized and develop into a baby, a man’s sperm keeps dividing throughout his life, increasing the chance of mutation.
Some studies suggest that children of older mothers benefit because they are nurtured more at home. If that is the case, then it appears that children of older fathers don’t experience this benefit.
But this study cannot answer these questions, it can only point to the need for more research, and perhaps emphasize the importance of doing so, especially as the trend toward older fatherhood appears likely to continue.
“Advanced Paternal Age Is Associated with Impaired Neurocognitive Outcomes during Infancy and Childhood.”
Saha S, Barnett AG, Foldi C, Burne TH, Eyles DW, Buka SL and McGrath JJ.
PLoS Medicine Vol. 6, No. 3, e40. Published online March 10, 2009.
doi:10.1371/journal.pmed.1000040
Sources: Journal article and editor’s comments.
Written by: Catharine Paddock, PhD