Women exposed to high levels of passive smoking have an increased risk of experiencing infertility, according to research.

The study of 88,732 postmenopausal women found that those who were active smokers were 14 percent more likely to have problems conceiving.

However, similar observations were also made for women who had never smoked but reported prolonged exposure (more than 10–20 years) to secondhand smoke at high levels. These women were 18 percent more likely to experience problems conceiving than women who had never been exposed to secondhand smoke.

'This is one of the first studies of this size and statistical power to investigate and quantify active and passive smoking and women's health issues. It strengthens the current evidence that all women need to be protected from active and passive tobacco smoke,' the researchers write in Tobacco Control.

The study used questionnaire data from the Women's Health Initiative Observational Study during 1993–1998. Women reported whether they had ever sought medical attention for infertility, defined as being unable to conceive following one year of unprotected sexual intercourse in the absence of male-factor infertility.

Lead researcher, Andrew Hyland, from Roswell Park Cancer Institute in Buffalo, New York, told Reuters Health that earlier studies had linked smoking to reproductive issues in women, but few had looked at links between secondhand smoke and infertility. 'The literature really wasn't clear – particularly with secondhand smoke,' Hyland commented.

Their findings remained after other factors that influence fertility (such as body mass index at 18 years of age, alcohol consumption, and other lifestyle and socioeconomic factors) were taken into account.

However, the researchers note that the association between passive smoking and infertility does not prove causation, as there may be other unknown factors involved and further investigation is needed 'due to the current gaps in the literature on this topic'.

The researchers also replicated a previously known association between smoking and earlier menopause. Active smokers reached menopause at a mean age of 47.6 years compared with 49.4 among never smokers who had not been exposed to secondhand smoke. Women with the greatest exposure to secondhand smoke also went through the menopause an average of 13 months earlier than non-exposed women.

An estimated 4000 compounds in cigarette smoke affect fertility and can negatively impact physiological processes such as hormone levels and embryo implantation.

Speaking to WebMD, Patricia Folan, director of the North Shore-LIJ Center for Tobacco Control in New York, commented: 'The findings are a valuable reminder to avoid all smoke. This evidence, in addition to the data from the current study, offers health care providers, particularly ob-gyn practitioners, the information needed to counsel women about the hazards of smoking and secondhand smoke, and to encourage cessation.'

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.