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. This may also be important in the transmission of other exposures and diseases."

Rates of childhood asthma have increased rapidly in the last 50 years and experts suspect environmental exposures may be behind the trend.