Dads who smoke raise the risk of their children and even grandchildren developing attention deficit disorders and hyperactivity, suggests a new study.
Researchers found that a father’s nicotine use may cause cognitive deficits in future generations because it damages sperm.
They say the effect, which was not caused by direct secondhand exposure, may be due to epigenetic changes in key genes in the father’s sperm.
Exposure of mothers to nicotine and other components of cigarette smoke is recognised as a significant risk factor for behavioural disorders – including attention deficit hyperactivity disorder (ADHD) in multiple generations of descendants.
Whether the same applies to fathers has been less clear, in part because in human studies it has been difficult to separate genetic factors – such as a genetic predisposition to ADHD – from environmental factors, such as direct exposure to cigarette smoke.
To overcome the difficulty, researchers at Florida State University in the US exposed male mice to low-dose nicotine in their drinking water during the stage of life in which the mice produce sperm.
They then bred the mice with females that had never been exposed to nicotine.
While the fathers were behaviourally normal, both sexes of offspring displayed hyperactivity, attention deficit, and cognitive inflexibility.
When female – but not male – mice from this generation were bred with nicotine-naïve mates, male offspring displayed fewer, but still significant, deficits in cognitive flexibility.
Analysis of sperm from the original nicotine-exposed males indicated that promoter regions of multiple genes had been epigenetically modified, including the dopamine D2 gene, critical for brain development and learning.
The researchers said that it suggests that the modifications likely contributed to the cognitive deficits in the descendants.
Nicotine and cigarette smoke have been previously shown to cause widespread epigenetic changes, said the researchers.
Study leader Professor Pradeep Bhide added: “The fact that men smoke more than women makes the effects in males especially important from a public health perspective.
“Our findings underscore the need for more research on the effects of smoking by the father, rather than just the mother, on the health of their children.”
The findings were published in the journal PLOS Biology.