Children born to older fathers perform less well in intelligence tests during infancy and early childhood, research shows, adding to the body of evidence linking paternal age to neuro-developmental disorders in offspring.
But children born to older mothers gain higher scores in the same tests, designed to measure the ability to think and reason, memory and concentration, and motor skills.
The University of Queensland researchers said the surprising results were a clear warning to the growing number of men in Western societies who are delaying parenthood until their 40s or older.
While public health messages have tended to focus on problems associated with ageing mothers, the study's lead author, Professor John McGrath from the Queensland Brain Institute at the university, said biological clocks were also ticking for men.
"The results were quite startling as it was thought that the age of the father was less of a concern compared to the age of the mother," Professor McGrath said. "Now we are getting more evidence of the age of the father being just as important."
The research, published in the medical journal PLoS Medicine yesterday, re-analysed data from one of the largest studies of children in the US, the Collaborative Perinatal Project.
More than 33,000 children were tested at eight months, four years and seven years on a variety of intelligence tests, and researchers factored in maternal age and socio-economic differences in the study.
The authors said in contrast to their father's age, children of older mothers performed better in intelligence tests, which could be put down to socio-economic factors or because these children experienced a more nurturing home life.
In an accompanying commentary, Mary Cannon from the Department of Psychiatry at the Royal College of Surgeons in Ireland argues that advanced paternal age has a wider range of effects on the health and development of a child than increased maternal age, which is largely confined to a heightened risk for Down syndrome.
Evidence shows older fathers are more likely to produce childhood conditions such as cleft lip and palate, childhood cancers and congenital heart defects, and neuro-psychiatric conditions such as schizophrenia, bipolar disorder, autism and epilepsy.
Professor McGrath said scientists suspected that older men were more likely to produce sperm containing an increased number of mutations, and these DNA errors are passed on to offspring.
Unlike women, men remain fertile and continued producing sperm even in old age.
"These mistakes then pile up and increase the risks of problems in the children, and it is possible that these mistakes will carry on into the next generation," Professor McGrath said.
But a professor of psychology at Curtin University of Technology, David Hay, cautioned against blaming a genetic mechanism, saying a more mundane explanation such as the limited time older fathers may have to interact with their children could be the cause.
"They may have less energy and possibly more work commitments and, of course, there may be older children which dilutes further their time to spend with the young child," he said.
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