Boys who smoke in their early teenage years risk damaging the genes of their future children, increasing their chances of developing asthma, obesity and low lung function, a new study has said.

Researchers from the UK-based University of Southampton and the University of Bergen in Norway investigated the epigenetic profiles of 875 people, aged 7 to 50, and the smoking behaviours of their fathers.

They found epigenetic changes at 19 sites mapped to 14 genes in the children of fathers who smoked before the age of 15. 

These changes in the way DNA is packaged in cells (methylation) regulate gene expression (switching them on and off) and are associated with asthma, obesity and wheezing.

"Changes in epigenetic markers were much more pronounced in children whose fathers started smoking during puberty than those whose fathers had started smoking at any time before conception," said Dr. Negusse Kitaba, Research Fellow at the University of Southampton. 

"Early puberty may represent a critical window of physiological changes in boys. This is when the stem cells are being established which will make sperm for the rest of their lives," Kitaba added.

According to Dr Gerd Toril Morkve Knudsen from the University of Bergen and co-lead author of the study, 16 of the 19 markers associated with father’s teenage smoking had not previously been linked to maternal or personal smoking. 

This suggests these new methylation biomarkers may be unique to children whose fathers have been exposed to smoking in early puberty.

"Our studies have shown that the health of future generations depends on the actions and decisions made by young people today long before they are parents -- in particular for boys in early puberty and mothers/grandmothers both pre-pregnancy and during pregnancy," said Professor Cecilie Svanes from the University of Bergen.

The new findings have significant implications for public health. They suggest a failure to address harmful exposures in young teenagers today could damage the respiratory health of future generations, further entrenching health inequalities for decades to come.