(Reuters Health) - Nonsmoking women who were exposed to secondhand smoke as children may have an increased risk of a miscarriage, a Chinese study suggests.

A woman lights a cigarette in this illustration picture taken in Paris, October 8, 2014. REUTERS/Christian Hartmann

Although they had never been smokers themselves, women in the study who lived with two or more smokers as a child had a 20 percent higher risk of miscarriage, and those who were exposed to smoke five or more times per week had a 14 percent greater risk of losing a pregnancy, compared to women not exposed to secondhand smoke in childhood.

Nonsmokers who grew up with one smoker in the house, or were around smoke less than five times per week, didn’t appear to have any change in their miscarriage risk.

“Our findings support the enactment of stringent national smoke-free laws and strict enforcement in China, and promotion of smoke-free homes to protect children, as well as the need for campaigns to change social norms of smoking and passive smoking,” the authors wrote in Tobacco Control.

Shanshan Yang, a researcher at the Institute of Geriatrics at the Chinese PLA General Hospital in Beijing, and colleagues analyzed survey data for almost 20,000 women age 50 and older who live in Guangzhou, China.

About 57 percent of the women had been exposed to secondhand smoke during childhood, that is, before age 18.

The study had some limitations because the participants had to rely on memories of childhood, and the researchers were not able to assess how old the women were when they had their miscarriages or if they were exposed to secondhand smoke during their pregnancies.

Lucy Popova, a researcher with the Georgia State University School of Public Health in Atlanta, said there are considerable differences in smoking habits between the U.S. and China.

“In the U.S., smoking rates between men and women are pretty close; in China, very few women smoke while a majority of men smoke. There are also other factors (indoor smoking policies and rules, social norms) that might affect the rates of exposure to secondhand smoke in childhood,” she said.

However, Popover said the potential biological mechanisms linking secondhand smoke exposure and pregnancy loss would be the same no matter where the mother lives.

“So while a study might find different numbers of women with heavy childhood exposure to secondhand smoke, the relationship between exposure and pregnancy loss most likely will still be there,” she said.

She pointed out that three other studies, conducted in the U.S. and cited in the new report, have also shown that childhood secondhand smoke exposure is linked with pregnancy loss.

Popova added that according to the U.S. Surgeon General, there are no safe levels of exposure to secondhand smoke, even brief exposure causes immediate harm, and the only way to protect nonsmokers from the dangerous chemicals in secondhand smoke is to eliminate smoking indoors.

The authors of the report didn’t respond to a request for comment.

SOURCE: bit.ly/2j1dieP Tobacco Control, online December 23, 2016.