Women who smoke may enter menopause about a year earlier than non-smokers, according to a new meta-analysis.
Study author Dr 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 report that pooled data from six studies of roughly 6,000 women in the US, Poland, Turkey and Iran show that non-smokers reached menopause between 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.
Dr Dvornyk and his colleagues also analysed five other studies that used a cut-off age of 50 or 51 to stratify women into early and late menopause groups. Among the more than 43,000 women in that analysis, smokers were 43% more likely than non-smokers to have early menopause.
Associated health problems
"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 a report published online in Menopause.
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," Dr 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.
Dr Jennie Kline, an epidemiologist from Columbia University's Mailman School of Public Health in New York, said there are two theories why smoking might mean earlier menopause.
Smoking kills eggs
Smoking may have an effect on how women's bodies make, or get rid of, oestrogen, she said. Alternatively, some researchers believe certain components of cigarette smoke might kill eggs.
Dr 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.
Better reasons to stop smoking
Alcohol, weight and whether or not women have given birth may each also play a role in the timing of menopause – but the evidence for everything other than smoking has been mixed, according to Dr Kline, who was not involved in the new study.
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 in their late thirties, or whether they have trouble with infertility.
Still, Dr Kline said, "There are way better reasons to stop smoking than worrying about menopause."
(Reuters Health, October 2011)