Gene mutations tend to be more common in older fathers
Children of older fathers perform less well in a range of brainpower tests during infancy and early childhood, a study found.
In contrast, children with older mothers did well on the tests, which assessed abilities such as memory, learning and concentration.
Experts believe mutations in a man's sperm, which build over time, may be a factor.
The University of Queensland study appears in the journal PLoS Medicine.
The age at which men and women are having children is increasing in the developed world.
But while the effect of increasing maternal age on reduced fertility is widely known, the impact of increased paternal age is not as well established.
However, older fathers have been linked to a range of health problems, including an increased risk of birth deformities, autism and neuropsychiatric conditions, such as schizophrenia and bipolar disorder.
The Queensland team analysed data on 33,437 children born between 1959 and 1965 in the US.
Each child was given a range of tests of cognitive function at eight months, four years, and seven years.
The researchers adjusted their study to take account of socio-economic factors, such as family income and parental education.
They found that the older the father, the more likely the child was to have lower scores on the various tests.
In contrast, the older the mother the higher the scores of the child in the cognitive tests.
Previous researchers have suggested children of older mothers may perform better because they experience a more nurturing home environment.
But the latest study suggests this might not be the case in relation to fathers.
Genetic factors are likely to be key, as there is evidence that genetic mutations become more widespread in a man's sperm as he ages.
But the Queensland team said the impact of social factors could also not be ruled out, although they said a child would usually benefit socioeconomically from having an older father, with better access to health and educational services.
The researchers, led by Dr John McGrath, wrote: "Given the trend towards older maternal and paternal ages in the developing world, policy-makers may want to consider promoting an awareness of the risks to children that this study associates with delayed fatherhood."
Dr Allan Pacey, an expert in fertility at the University of Sheffield, said: "We have known for some time that the children born from older fathers are at increased risk of a number of medical problems and this is almost certainly because as men get older the sperm production gets less efficient and their sperm have a higher number of genetic defects.
"The author's observation that most neurocognitive outcomes is also reduced in the children of older fathers provides a further piece of evidence to remind us that nature intended us to have our children earlier in our lives than we currently are."