BMC Public Health 2007, 7:149 http://www.biomedcentral.com/1471-2458/7/149 were not much affected. Thus only the crude ORs are pre- sented in table 1. Table 2 presents data of the association between meno- pause and stimulants (smoking, coffee and alcohol). Cur- rent active smoking showed an association with early menopause when adjusted for education (adj. OR, 1.59; 95% CI, 1.11–2.28). This association did not change after further adjustment for the intake of coffee and alcohol, but when adjusting in addition for marital status, educa- tional level, social participation, self reported health and coffee consumption the adj. OR is 1.33 and 95% CI 0.85– 2.08. To drink more than four cups of coffee a day showed an association with early menopause (OR, 1.83; 95% CI, 1.07–3.14), but this association disappeared when adjust- ing for the other variables shown to be related with the end point (adj. OR 1.58; 95% CI 0.88–2.83, data not shown) or the two other stimulants (adj. OR 1.31; 95% CI 0.73–2.37) (table 2). A part from being borderline signif- icantly negatively associated with menopause in the crude analyses, alcohol consumption showed no association with the onset of menopause (table 2). Table 3 shows the associations between active smoking and early menopause. The number of cigarettes smoked daily (adj. OR, 1.48; 95% CI, 1.03–2.13) was positively associated with early menopause and even shows a dose- response relationship. A test for linear trend turned out positive (p-value = 0.04). The number of years between smoking cessation and the age of menopause was also sig- nificantly associated with age of menopause (Table 3); women who had stopped smoking more than 10 years before menopause had a lower risk of early menopause than did those still smoking at the start of menopause (adj. OR, 0.13; 95% CI, 0.05–0.33). Total exposure to smoking analysed among current and former smokers, was positively related to the age of menopause, and women at the highest doses had nearly double the odds of early menopause (adj. OR, 1.79; 95% CI, 1.06–3.02). The ORs in Table 3 were changed by 0.1–0.4 by inclusion of marital status, educational level, social participation, self reported health and coffee consumption as covariates. The most pronounced change was seen for high total exposure to smoking (adj. OR 1.47 (95-% CI 0.77–2.79). The result concerning smoking cessation was practically not changed (adj. OR 0.13; 95-% CI 0.05–0.36 by cessa- tion of smoking >10 years prior to menopause). Separate analysis of those smoking at the age of meno- pause showed an inverse association between the number of years of active smoking and early onset of menopause (OR, 0.89; 95% CI, 0.86–0.92, adjusted for education, data not shown). Age of starting to smoke on a daily basis was not associated with early menopause. Passive smoking recorded among non-smokers was not significantly associated with early menopause except for a borderline significant association of parents' smoking when growing up (Table 4). The inclusion of other varia- bles presented in Table 1 as covariates did not change the significance levels. Discussion Our study of postmenopausal women is population based with a high proportion of smoking participants. Our main finding was that current active smoking is related to early menopause, and that smoking cessation Table 2: Association between early menopause and smoking and intake of coffee and alcohol Variable % with early menopause and total number that answered Crude OR 95% CI Adj. OR a 95% C.I. Adj. OR b 95% CI Smoking Never Earlier Current Coffee (cups per day) 0 1–4 >4 Alcohol consumption None in last year <1 time per week At least once per week % 7.8 9.2 13.4 7.9 8.8 13.6 12.2 10.5 8.4 N 963 609 514 280 1431 338 172 849 1083 Lower Upper Lower Upper Lower Upper Ref. 1.18 1.71 Ref. 1.15 1.83 Ref. 0.80 0.62 0.82 1.21 0.72 1.07 0.48 0.37 1.71 2.42 1.85 3.14 1.34 1.04 Ref. 1.16 1.59 Ref. 1.14 1.64 Ref. 0.93 0.78 0.80 1.11 0.70 0.94 0.55 0.46 1.68 2.28 1.86 2.88 1.59 1.34 Ref. 1.27 1.66 Ref. 1.09 1.31 Ref. 0.83 0.66 0.86 1.12 0.66 0.73 0.47 0.37 1.88 2.45 1.79 2.37 1.47 1.18 a Adjusted for educational level b Adjusted for the two other stimulants and educational level Page 4 of 8 (page number not for citation purposes)