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Women who are heavy or habitual smokers are more likely to experience the menopause earlier, a study suggests.
The report, involving 79,000 women, showed those who smoked from the age of 15 went through the menopause on average 21 months earlier than women who did not smoke.
The paper also found a weaker link with prolonged exposure to passive smoke.
Experts say the study adds to growing evidence that toxins in tobacco can harm overall reproductive health.
Hormone disruption
Writing in the journal Tobacco Control, a team of researchers looked at data from participants in the women's health initiative observational study.
All women involved in this paper had gone through the menopause when they were recruited to the investigation between 1993 and 1998.
Using questionnaires, they were asked how long they had smoked for, how much they smoked and when they had experienced the menopause.
Comparing smokers with women who had never smoked, researchers found those who said they smoked heavily (more than 25 cigarettes a day) were likely to have faced the menopause 18 months earlier than non-smokers.
And non-smokers who had experienced many years of exposure to passive smoke - for example living with indoor smokers - went through the menopause earlier than non-smokers who were not around tobacco.
Scientists say the findings stood true even when alcohol use, educational backgrounds, oral contraceptive prescriptions and ethnicity were taken into account.
They suggest toxins in tobacco may play a role by disrupting key reproductive hormones, including oestrogen.
And though they cannot be certain of the long-term health consequences of these findings, they point out that previous studies have linked earlier menopause to a risk of earlier death.
But early menopause has also been associated with a lower risk of certain diseases, including breast cancer.
'True phenomenon'
Separately, the study supported an established link between smoking and fertility problems.
Commenting on the findings, Prof Ashley Grossman, at the University of Oxford, said: "This is slightly worrying - there is only a slightly increased risk of infertility in smokers compared to never-smokers, but this new study suggests that so-called passive smokers might be similarly affected.
"Maybe more convincing is the nearly two-year earlier menopause in smokers and around one year in passive smokers; this dose-response effect does suggest we are looking at a true phenomenon."
Other experts point out that during the duration of the study, smoking was more common in both men and women.
But despite this researchers say their investigation, along with others, shows "all women need to be protected from active and passive smoke".
NHS Choices concluded from similar previous research that "while the link needs further testing, there are many proven benefits from stopping smoking".
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