Children whose grandmothers smoked have a heightened risk of asthma even if their mothers avoided the habit, a study has shown.
Evidence that the lifestyle sins of the grandmother can skip a generation and be visited upon her grandchildren comes from a large Swedish study.
It adds to growing evidence that “epigenetic” environmental influences can alter genetic activity in ways that may be inherited, leading to health problems that emerge in offspring.
Smoking is one environmental factor known to affect the activity, or “expression”, of genes.
Dr Caroline Lodge, one of the study authors from the University of Melbourne in Australia, said: “We found that smoking in previous generations can influence the risk of asthma in subsequent generations.”
Rates of childhood asthma have increased rapidly in the last 50 years, and experts suspect environmental exposures may be the cause.
For the study, researchers analysed data on 44,853 Swedish grandmothers who were asked if they smoked during pregnancy.
Use of asthma medication was also recorded in 66,271 grandchildren and the two sets of results compared.
The investigation showed that if grandmothers smoked while pregnant, the risk of their grandchildren having asthma was raised by 10% to 22%, even if the children’s mothers did not smoke.
Co-author Professor Bertil Forsberg, from Umea University in Sweden said: “The next stage for the research team is to investigate the potential inheritance of asthma risk through the male line, by assessing the risk of asthma in grandchildren whose grandmothers smoked while pregnant with their fathers.
“The findings also encourage research into inherited disease risks for other environmental exposures.”
Asthma prevalence is believed to have plateaued since the late 1990s after previously rising steeply.
Dr Lodge said: “For us to understand more about the asthma epidemic, we require a greater understanding of how harmful exposures over your lifetime may influence the disease risks of generations to come.
"Additionally, researchers need to be aware, when interpreting the asthma risk from current exposures and genetic predisposition, that individuals may carry an inherited, non-genetic risk from exposures in previous generations.
Dr Samantha Walker, director of research and policy at Asthma UK, said: “ Studies like this help us to understand the roles genes play and how we can find better treatments and ultimately a cure.”
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