Nobody should need another reason not to smoke while pregnant, but researchers have found one: A study that looked at tens of thousands of grandmothers and grandchildren in Sweden found that children whose maternal grandmothers smoked were up to 22% more likely to have asthma, even if their mothers never took up the habit, Discovery reports. Researchers knew that nicotine exposure caused genetic changes in animals that could be passed down through generations, and the study set out to determine whether the same "epigenetic inheritance" happened with humans who smoke, reports WebMD.
"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," study co-author Caroline Lodge says in a press release. The researchers say the inheritance of risk could help explain why there has been a steep rise in asthma cases over the last 50 years, even though smoking rates have declined. They now plan to investigate whether the same risk is passed down through the male line by looking at people whose grandmothers smoked when they were pregnant with their fathers. (Canadian researchers found that the stress of women who were pregnant during an ice storm showed up in their children's DNA.)