NEW YORK - Women who smoke may hit menopause about a year earlier than those who don't light up, according to a new look at past research.
That's important because the age at which women stop getting their periods may influence their risk of bone and heart diseases as well as breast cancer.
Study author Volodymyr Dvornyk, from the University of Hong Kong, said that women "should be aware of this effect and possible health consequences" of smoking, in addition to its other known risks.
He and his colleagues scanned the literature and found that women who were current smokers hit menopause a year earlier, on average, than non-smokers.
That data came from six studies including about 6,000 women in the US, Poland, Turkey and Iran. Non-smokers hit menopause between age 46 and 51, on average, depending on the study population. In all but two of the studies, smokers were younger -- between 43 and 50, overall.
Dvornyk and his colleagues also analyzed five other studies that used a cut-off age of 50 or 51 to group women into "early" and "late" menopause. Out of more than 43,000 women in that analysis, women who smoked were 43% more likely than nonsmokers to have early menopause.
"Our results give further evidence that smoking is significantly associated with earlier (age at menopause) and provide yet another justification for women to avoid this habit," the researchers wrote in the journal Menopause.
Both early and late menopause have been linked to health risks. Women who hit menopause late, for instance, are thought to be at higher risk of breast cancer because one risk factor for the disease is more time exposed to estrogen.
However, the "general consensus is that earlier menopause is likely to be associated with the larger number and higher risk of postmenopausal health problems, such as osteoporosis, cardiovascular diseases, diabetes mellitus, obesity, Alzheimer's disease, and the others," Dvornyk told Reuters Health in an email.
Overall, he added, early menopause is also thought to slightly raise a woman's risk of death in the years following.
Jennie Kline, an epidemiologist from Columbia University's Mailman School of Public Health in New York, said there are two theories for why smoking might mean earlier menopause.
Smoking may have an effect on how women's bodies make, or get rid of, estrogen, she said. Alternatively, some researchers believe certain components of cigarette smoke might kill eggs.
Dvornyk's team didn't have information on how long women had been smoking or how many cigarettes they smoked each day, so the researchers couldn't determine how either of those factors may have affected age at menopause.
For that reason, and a lack of data on other health and lifestyle factors linked to menopause, this analysis may not be enough to resolve lingering questions on the link between smoking and menopause, they added.
Alcohol, weight and whether or not women have given birth may each also play a role in when they hit menopause -- but the evidence for everything other than smoking has been mixed, Kline, who was not involved in the new study, told Reuters Health.
She said it's possible the same factors that influence age at menopause may determine whether or not women are still able to get pregnant when they hit their late thirties, or whether they have trouble with infertility.
Still, Kline said, "There are way better reasons to stop smoking than worrying about menopause," such as reducing the risk of heart disease and lung cancer.