Active and passive smoking were found to increase women's risk of infertility and earlier menopause in the latest study.
Study coauthor Andrew Hyland, of the Roswell Park Cancer Institute in Buffalo, NY, and colleagues publish their findings in the journal Tobacco Control.
Previous research has also associated tobacco use with infertility and earlier menopause in women. However, Hyland and colleagues note that it was unclear whether secondhand smoke exposure poses the same risks.
To find out, the team analyzed the tobacco exposure of 93,676 women aged 50-79 who were part of the Women's Health Initiative Observational Study (WHI OS). All women were enrolled to the study between 1993-1998.
Women who were current or former smokers were asked the age at which they started smoking, how many years they had smoked and how many cigarettes they smoked daily.
Women who had never smoked were asked whether they had ever lived with a smoker during childhood and adulthood, and for how long, and whether they had ever been exposed to tobacco smoke in the workplace.
Fertility data was available for 88,372 women and their partners, while 79,690 women had experienced a natural menopause - defined as the absence of a period for 12 consecutive months without having undergone surgery to remove the ovaries.
Passive smoking linked to 18% greater risk for infertility
Infertility - defined in the study as trying for a baby for at least 12 months, seeking medical advice and the male partner not being a cause - was reported by 15.4% (13,621) of the 88,372 women.
Around 45% (35,834) of the women who had experienced a natural menopause said they had gone through the transition before the age of 50; the average age of menopause is 51.
- Around 40 million American adults currently smoke
- Around 15 in every 100 American women currently smoke
- Since 1964, around 2.5 million non-smokers are estimated to have died from health problems caused by secondhand smoke exposure.
Compared with women who had never smoked, the team found that women who were either current or former smokers were at 14% greater risk for infertility and at 26% greater risk of experiencing menopause before the age of 50.
Women with the highest tobacco use who began smoking before the age of 15 experienced menopause an average of 22 months earlier than never-smokers who had never been exposed to secondhand smoke.
Women who smoked a minimum of 25 cigarettes daily had menopause around 18 months earlier than those who had never smoked.
But it was not only active smokers who were found to be at increased risk of infertility and earlier menopause; never-smokers who had been exposed to high levels of secondhand smoke were also at risk.
Women with the highest levels of passive smoking - at least 10 years of living with a smoker in childhood, at least 10 years working with smoking colleagues, or at least 20 years living with a partner who smoked at home - were at 18% greater risk of infertility than those who had never been exposed to secondhand smoke.
Menopause arrived around 13 months earlier for women with the highest levels of secondhand smoke exposure, compared with those who had the lowest levels of exposure to passive smoking.
The team's findings remained even after accounting for a number of influential factors, such as educational attainment, body mass index (BMI) at age 18, physical activity levels, exposure to insecticides, use of oral contraceptives and age at first menstrual cycle.
'All women should be protected from active, passive tobacco smoke'
Though the team did not investigate the mechanisms by which tobacco exposure may lead to infertility and earlier menopause, they say previous research has shown that toxins in tobacco smoke can interfere with reproductive and hormonal processes.
It is unclear whether earlier menopause has any clinical implications, though previous studies have associated earlier menopause to greater risk of all-cause mortality, the team notes.
This observational study cannot prove a causal link between tobacco exposure and greater risk of earlier menopause and infertility, but the team says their findings support smaller studies that have shown a similar association.
The authors write:
"It 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."
There are some limitations to the study. For example, data on women's infertility problems and age at menopause were self-reported, meaning the findings were open to recall bias.
Additionally, the researchers say they were unable to completely rule out male partners as a cause of infertility. "However," they add, "there is no reason to think that this would be differential between the exposure categories."
Medical News Today recently reported on a study linking smoking during pregnancy to poorer later-life aerobic fitness for male offspring.