The second is the effect of cigarette smoke on certain enzymes

Women who smoke are likely to undergo cat litter mould menopause at a younger age than nonsmokers,   according to the findings of two studies involving more than 3,500 middle-aged   women in seven countries.In fact, the studies showed, the more a woman smokes, the earlier her menopause   is likely to occur. The average age for menopause in women who have quit smoking   was found to fall between that of light smokers (half a pack a day) and that   of women who never smoked.Most women in developed countries stop menstruating between the ages of 44   and 54, with the average age around 50. In one of the studies, the researchers   found that at ages 48 to 49, a woman who smokes a pack or more a day is nearly   twice as likely to be past menopause as a woman who never smoked. At ages 50   to 51, 79 per cent of the women who smoked a pack or more a day were past menopause,   as against 56 per cent of those who never smoked.This "striking association" between smoking and the onset of menopause   was accidentally discovered as part of a continuing international research project,   the Boston Collaborative Drug Surveillance Program.

The researchers, Dr. Hershel   Jick and Jane Porter of Boston University School of Medicine and Dr. Alan S.   Morrison of the Harvard School of Public Health, said they noticed the relationship   while exploring the link between smoking and heart disease.A closer look at the data suggested to the researchers that smoking might actually   precipitate earlier menopause. At each age, the women in the studies who were   smokers were more likely to be past menopause than those who had never smoked   and the heavy smokers were more likely to be past menopause than the light smokers.   The association between smoking and earlier menopause was similar in all the   countries involved. The researchers said they could discern no other factors   to account for the finding.Writing in the British medical journal The Lancet, the researchers suggested   two possible mechanisms for the link between smoking and menopause. One is the   effect of nicotine on the central nervous system, possibly resulting in changes   in the secretion of hormones involved in the menopause.

The second is the effect of cigarette smoke on certain enzymes that may in turn influence the way the   body handles the sex hormones.The researchers said the effect of smoking on the onset of menopause might   account for the association previously found between menopause and heart disease.   Women post menopause have been   shown to have a higher rate of coronary heart disease than premenopausal women   of the same age. But since smoking is known to increase a person's chance of   developing heart disease and has now been shown to accelerate the onset of menopause,   smoking rather than menopause itself may be the real explanation for the heart   disease statistics, the Boston researchers suggested.

Each of the 3,534 women who participated in the two studies was interviewed   by a specially trained nurse, as to her personal habits, menopausal status and   past medical and medication history, as well as such demographic characteristics   as age, marital status and number of children.The women were part of two much larger studies involving a total of 57,000   patients treated at 24 hospitals in Boston and at hospitals elsewhere in the   US and six other countries. The smoking-menopause   analysis excluded all women who had had their ovaries removed surgically and   whose menopausal status or smoking status was uncertain at the time of the interview.

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