Grandmothers who smoke while pregnant may put their grandchildren at risk.
According to the Centers for Disease Control and Prevention (CDC), asthma now affects 8% of adults and 9.3% (6.8 million) of children in the US, and prevalence has increased rapidly in the past 50 years.
Changing environmental exposures have been thought to be responsible, but more recently, researchers have started looking to previous generations for clues, with increasing evidence that grandmothers are to blame.
The current study, based in Sweden, is the first to investigate the risk in a whole population and to use evidence taken directly from grandmothers at the time they were pregnant.
Asthma risk increased 10-22% if grandmother smoked
The survey covered 44,853 grandmothers listed with the Swedish Registry from 1982-86. Smoking exposure was recorded during pregnancy, and use of asthma medication was recorded in 66,271 grandchildren.
The results showed children had an increased asthma risk of 10-22% if their grandmothers smoked during pregnancy, even if their mothers had not.
It is known that environmental exposures such as tobacco can affect the activity of genes through a process known as "epigenetic modification." It is becoming increasingly evident that these changes can be passed to subsequent generations or remain dormant until a future generation, and specifically with reference to tobacco and asthma.
Dr. Caroline Lodge, one of the study's authors and Research Fellow at the University of Melbourne, Australia, says:
"We found that smoking in previous generations can influence the risk of asthma in subsequent generations. This may also be important in the transmission of other exposures and diseases."
Dr. Lodge adds that to understand the asthma epidemic, is it important to know how harmful exposures in the present may affect generations to come. She calls on researchers, when assessing asthma risk from current exposures and genetic predisposition, to bear in mind that there may be an inherited, nongenetic risk carried over from exposure in previous generations.
Researchers in the US have previously hypothesized that this multigenerational transmission could account for why 98% of inherited human diseases are unaccounted for by the prevailing view of genetic trait transmission, known as Mendelian genetics.
So far, scientists have focused on children whose grandmothers smoked while pregnant with their mothers. The next step, according to Prof. Bertil Forsberg, presenting author of the study from Umeå University, Sweden, is to research the effect of grandmothers smoking while pregnant with boys who become fathers. He also suggests further study into inherited disease risks for other environmental exposures.
In a previous article published by Medical News Today, a link was suggested between childhood asthma and fathers smoking prior to conception.