Stress of daily activities and risk of breast cancer: A prospective cohortstudy in Finland

The belief that life stress enhances breast cancer is common, but there are few prospective epidemiological studies on the relationship of life stress and breast cancer. We have investigated the association between stress of daily activities (SDA) and breast-cancer risk in a prospective cohort study of 10,519 Finnish women aged 18 years or more. SDA measures a subject's ow n appraisal of daily stress. It was assessed in 1975 and 1981 by a self-adm inistered questionnaire, which also provided information on subject charact eristics and other known breast-cancer risk factors, Follow-up data for bre ast cancer from 1976 to 1996 were attained through record linkage to the Fi nnish Cancer Registry. Study subjects were divided into 3 groups based on t heir SDA scores in 1975: no stress (23% of subjects), some stress (68%) and severe stress (9%), Hazard ratios (HRs) and respective 95% confidence inte rvals (Cls) for incidence of breast cancer by level of SDA were obtained fr om the Cox proportional hazards model, We identified 205 incident breast ca ncers in the cohort. Multivariable-adjusted HRs for breast-cancer risk were 1.00 (reference), 1.11 (95% Cl 0.78-1.57) and 0.96 (95% Cl 0.53-1.73) by i ncreasing level of stress, Neither shifting of the SDA cut-off points nor r estricting the analysis to women who reported the same level of SDA in 1975 and 1981 materially altered the results. We found no evidence of an associ ation between self-perceived daily stress and breast-cancer risk. (C) 2001 Wiley-Liss, Inc.