BMC Public Health 2007, 7:149 http://www.biomedcentral.com/1471-2458/7/149 was categorized as: married, unmarried, widowed, or divorced or separated. Social participation was measured by the number of for- mal or informal organizations or clubs they belonged to. Low participation was defined as no membership, normal participation as membership in 1–3 organizations or clubs, and high participation as involvement in >3 organ- izations or clubs. Body weight (to the nearest 100 g) and height (to the nearest mm) was measured with an electronic height and weight scale. Body mass index (BMI) was obtained by dividing body weight in kg by height in m2. According to WHO standards, BMI < 18.5 was considered underweight, 18.5–24.9 normal weight, 25–29.9 overweight and ≥30 obese [20]. The participants were asked how many hours a week they performed physical activity that made them sweat or out of breath. Based on their answer, they were divided into four groups (no such physical activity, ≤ 1 hour, 1–2 hours and ≥ 3 hours). Data were analysed using SPSS 12.0 for Windows. We applied logistic regression analysis (crude and adjusted OR) and set the level of significance as p < 0.05 and 95% CI. The associations were adjusted for potential con- founders, including education and selected lifestyle fac- tors. The potential interaction of education with smoking was investigated by including the product term of these factors in the regression analysis, which was non-signifi- cant. Results In this cohort, the mean age of menopause was 50.1 years and the median age was 50 years. The range was 40–61 years. The 25th percentile was 48 years and the 75th per- centile was 53 years. In all, 9.6% of the women had early menopause. In this group active and passive smoking was frequent. 24.2% were current smokers, 28.7% were former smokers and 35.2% were defined as passive smokers. Table 1 presents the crude associations between early menopause and selected risk factors. Women with a higher educational level were less likely to have entered menopause at an early stage (OR, 0.37; 95% CI, 0.23– 0.60). At the same time the women with the highest level of education are the ones the least exposed to smoking. Among the ones with more than 12 years of education, the percentage of never smokers is 54.0% and the percent- age of current smokers is 16.9%. These same percentages among the women with less than 8 years of education are respectively 40.8% and 33.1%. Being widowed as com- pared to being married almost doubled the odds for early menopause (OR, 1.89; 95% CI, 1.18–3.02), and a self- reported worse general health showed a similar associa- tion (OR, 1.83; 95% CI, 1.36–2.47). Other variables, such as age at menarche, parity, BMI or physical activity were not significantly correlated with age of menopause. Adjustment in relevant analyses for mari- tal status, educational level, social participation, self reported health and coffee consumption changed the point estimates by 0.1–0.2, but the significance levels Table 1: Association between early menopause (40–44 years) and selected variables Variables Crude OR 95% CI % with early menopause and total number that answered % N Marital status Married 8.5 1186 Unmarried 7.4 204 Widowed 15.2 171 Divorced or 10.9 558 separated Parity 0 9.9 304 1–3 9.8 1618 >3 7.1 168 Age at menarche 12–15 9.1 1773 <12 12.5 168 >15 11.5 182 Years of education <8 18.4 163 8–10 10.3 630 11–12 9.6 426 >12 7.3 874 Social participation Low 11.3 964 Medium 8.3 931 High 5.4 148 Self reported health Good 7.8 1354 Bad 12.9 728 Body mass index 18.5–24.9 9.3 965 <18.5 16.8 18 25.0–29.9 9.8 724 ≥30 9.5 367 Physical activity (hours per week) 0 10.7 844 <1 8.7 412 1–2 7.6 406 ≥3 10.8 167 Ref. 0.79 1.89 1.32 Ref. 1.03 0.72 Ref. 1.44 1.36 Ref. 0.51 0.50 0.37 Ref. 0.72 0.49 Ref. 1.83 Ref. 1.95 1.12 1.13 Ref. 1.02 0.79 0.70 Lower Upper 0.45 1.18 0.94 0.68 0.36 0.88 0.83 0.32 0.30 0.23 0.53 0.23 1.36 0.55 0.81 0.74 0.59 0.43 0.38 1.39 3.02 1.86 1.56 1.45 2.35 2.22 0.82 0.83 0.60 0.98 1.04 2.47 6.98 1.56 1.70 1.75 1.44 1.30 Page 3 of 8 (page number not for citation purposes)