BMC Public Health 2007, 7:149 http://www.biomedcentral.com/1471-2458/7/149 Table 3: Association between early menopause and exposure to tobacco smoke Variable % with early menopause and total number that answered Crude OR 95% CI Adj. OR a 95% CI % N Lower Upper Lower Upper Number of cigarettes smoked daily 0 7.8 966 Ref. 1–10 9.7 610 1.24 0.86 >10 12.1 514 1.54 1.08 Total smoking exposure b Low exposure 7.2 334 Ref. Medium exposure 12.1 354 1.73 1.02 High exposure 13.2 364 1.82 1.08 Age when started daily smoking (current smokers. N = 514) <20 14.9 235 Ref. 20–24 14.0 164 0.97 0.55 >24 10.5 105 0.72 0.35 Age when started daily smoking (former smokers. N = 609) <20 10.5 286 Ref. 20–24 8.1 197 0.71 0.37 >24 6.4 110 0.58 0.25 Number of years before the age of menopause one stopped smoking (former smokers. N = 609) Smoking at the time of menopause 16.9 195 Ref 1–10 11.9 135 0.74 0.39 >10 2.3 256 0.14 0.06 1.78 2.21 2.94 3.06 1.73 1.50 1.35 1.37 1.42 0.34 Ref. 1.17 1.48 Ref. 1.70 1.79 Ref. 0.95 0.73 Ref. 0.68 0.59 Ref. 0.68 0.13 0.81 1.03 1.00 1.06 0.52 0.35 0.35 0.25 0.35 0.05 1.68 2.13 2.89 3.02 1.73 1.53 1.32 1.40 1.32 0.33 2.44 8.12 2.64 1.54 Page 5 of 8 (page number not for citation purposes) a) Adjusted for educational level b) Number of cigarettes per year × years smoked prior to menopausal age seems to protect against early menopause. The most important limitation of our study is that the women were 59–61 years when they participated in the survey and were asked about health and related habits in their current situation. Many of the factors examined at that age, including BMI, coffee and alcohol consumption and marital status, may not reflect the status of these fac- tors in the years before and around menopause. The reports on coffee and alcohol consumption or current Hours present in a room where people are smoking 0 7.6 802 1–6 9.2 76 >6 6.3 16 Smoking mother or father while growing up No 9.0 378 Yes 6.1 580 Living with smokers after the age of 20 No 7.7 533 Yes 8.2 417 a Adjusted for educational level Table 4: Association between early menopause and passive exposure to tobacco smoke among never smokers Variable % with early menopause and total number that answered Crude OR 95% CI Adj. OR a 95% CI % N Lower Upper Lower Upper smoking at the time of the survey were, however, probably representative for the status around menopausal age, and any misclassification of these variables would most prob- ably be non-differential. In the Tromsø Heart Study the relative validity of the question on coffee consumption per day was compared with a dietary history survey two years later and the answers agreed well for coffee as well as other food items used every day in easily recorded unites [21]. Also, the reproducibility of the Tromsø survey ques- tionnaire was studied by comparing it with a new ques- tionnaire assessment one year later, and the concordance Ref. 1.28 1.12 Ref 1.50 Ref. 1.07 0.56 0.14 0.90 0.66 2.94 8.99 2.50 1.73 Ref. 1.04 0.99 Ref. 1.56 Ref. 0.94 0.44 0.12 0.92 0.58