Women who smoke or are exposed to secondhand (passive) smoke may have an increased risk of experiencing fertility problems and going through the menopause at an earlier age, a new study has found.

US researchers analysed over 93,000 women, looking at their lifetime smoking habits, fertility history and age at the time of natural menopause. A natural menopause was defined as not having had surgery to remove the ovaries and the absence of periods for at least one year.

All of the women were aged between 50 and 79 and had already been through the menopause when the study began.

Current and former smokers were asked about their habit, including when they had started smoking and for how many years. Those who had never smoked were asked whether they had lived with a smoker as a child or adult, and whether they had ever worked in a job where colleagues smoked in the workplace.

The researchers found that those who had been exposed to smoking had an increased risk of infertility and an earlier menopause.

Current or former smokers had a 14% increased risk of infertility and a 26% increased risk of menopause before the age of 50 when compared with never smokers.

In fact, the average age of women starting the menopause was much younger among current and former smokers compared to never smokers who had not been exposed to passive smoking.

Those who smoked the most could expect to go through the menopause up to 22 months earlier than non-smokers. Those who smoked at least 25 cigarettes per day could expect to begin the menopause 18 months earlier.

Meanwhile, non-smokers who had been exposed to the highest levels of passive smoking, i.e. 10 or more years as a child living with a smoker, 20 or more years as an adult living with a partner who smoked or 10 or more years working with colleagues who smoked, had an 18% increased risk of suffering fertility problems compared to women not exposed to passive smoking.

The findings stood even after other factors were taken into account such as body mass index (BMI), oral contraceptive use and age at first period.

The researchers said that there are biological explanations for these findings. The toxins in tobacco smoke are known to have various harmful effects on many aspects of reproduction and are also known to disrupt hormone production and activity.

"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," they added.

Details of these findings are published in the journal, Tobacco Control.