Sleep duration and breast cancer: a prospective cohort study.

Breast cancer incidence has increased during recent decades for reasons that are only partly understood. Prevalence of sleeping difficulties and sleepiness has increased, whereas sleeping duration per night has decreased. We hypothesized that there is an inverse association between sleep duration and breast cancer risk, possibly due to greater overall melatonin production in longer sleepers. This population-based study includes information from women born in Finland before 1958. Sleep duration, other sleep variables, and breast cancer risk factors were assessed by self-administered questionnaires given in 1975 and in 1981. Breast cancer incidence data for 1976 to 1996 was obtained from the Finnish Cancer Registry. Hazard ratios (HR) and 95% confidence intervals (CI) were obtained from Cox proportional hazards models adjusting for potential confounders. Altogether, 242 cases of breast cancer occurred over the study period among the 12,222 women with sleep duration data in 1975. For these women, the HRs for breast cancer in the short (< or =6 hours), average (7-8 hours), and long sleep (> or =9 hours) duration groups were 0.85 (CI, 0.54-1.34), 1.0 (referent), and 0.69 (CI, 0.45-1.06), respectively. Analysis restricted to the 7,396 women (146 cases) whose sleep duration in 1975 and 1981 were in the same duration group (stable sleepers) yielded HRs of 1.10 (CI, 0.59-2.05), 1.0, and 0.28 (CI, 0.09-0.88), with a decreasing trend (P = 0.03). This study provides some support for a decreased risk of breast cancer in long sleepers.

Stressful life events and risk of breast cancer in 10,808 women: a cohort study.

The authors prospectively investigated the relation between stressful life events and risk of breast cancer among 10,808 women from the Finnish Twin Cohort. Life events and breast cancer risk factors were assessed by self-administered questionnaire in 1981. A national modification of a standardized life event inventory was used, examining accumulation of life events and individual life events and placing emphasis on the 5 years preceding completion of the questionnaire. Through record linkage with the Finnish Cancer Registry, 180 incident cases of breast cancer were identified in the cohort between 1982 and 1996. The multivariable adjusted hazard ratio for breast cancer per one-event increase in the total number of life events was 1.07 (95% confidence interval (CI): 1.00, 1.15). This risk estimate rose to 1.35 (95% CI: 1.09, 1.67) when only major life events were taken into account. Independently of total life events, divorce/separation (hazard ratio (HR) = 2.26, 95% CI: 1.25, 4.07), death of a husband (HR = 2.00, 95% CI: 1.03, 3.88), and death of a close relative or friend (HR = 1.36, 95% CI: 1.00, 1.86) were all associated with increased risk of breast cancer. The findings suggest a role for life events in breast cancer etiology through hormonal or other mechanisms.

Personality characteristics and the risk of breast cancer: a prospective cohort study.

Various personality characteristics have been suggested to increase the risk of breast cancer but reliable epidemiologic data on this issue are limited. We prospectively investigated the relationship between personality characteristics and the risk of breast cancer in 12,499 Finnish women aged 18 years or more. In health questionnaires in 1975 and 1981, these women completed at least one of the following personality scales: Eysenck extroversion, Bortner type A behaviour and author-constructed measure of hostility. They also reported about other potential breast cancer risk factors. From 1976-1996, 253 cases of breast cancer were identified by record linkage with the Finnish Cancer Registry. Proportional hazard models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). The multivariable HRs of breast cancer for women with intermediate level (scores 3-6) and high level (7-9) of extroversion in 1975 were 1.18 (95% CI 0.87-1.60) and 0.97 (95% CI 0.64-1.47), respectively, compared to those with low level (0-2). These results remained unaltered when the level of extroversion was determined as the average of the 1975 and 1981 reports. There was also no increase in breast cancer risk in relation to type A behaviour and hostility. Furthermore, we observed no substantial joint effects of personality characteristics on the risk of breast cancer. In conclusion, our data do not support the existence of an important role for personality in the aetiology of breast cancer. These findings are reassuring to those who have believed the contrary.

A prospective study of life satisfaction, neuroticism and breast cancer risk (Finland).

OBJECTIVE: To prospectively investigate whether life satisfaction and neuroticism, two measures reflecting aspects of anxiety/depression, are related to risk of breast cancer. METHODS: The study population comprised 12,032 women from the population-based Finnish Twin Cohort. Life satisfaction and neuroticism were assessed in health questionnaires in 1975 and 1981. During 21 years of follow-up, 238 cases of breast cancer were documented in the study cohort through record linkage to the Finnish Cancer Registry. RESULTS: After adjustment for age and other important covariates, the hazard ratios were 1.0 (reference), 0.9 (95% confidence interval 0.6-1.3) and 1.0 (0.7-1.6) by decreasing level of life satisfaction (satisfied, intermediate, dissatisfied), and 1.0 (reference), 1.0 (0.7-1.4) and 0.8 (0.6-1.2) by increasing level of neuroticism (low, intermediate, high). These results did not change after accounting for possible changes in the levels of life satisfaction and neuroticism between 1975 and 1981. The null results were also confirmed with the use of a nested case-control study within twin pairs that became discordant for breast cancer during the follow-up. CONCLUSIONS: Our data indicate that life satisfaction and neuroticism are not substantially associated with breast cancer risk. These findings provide epidemiological evidence against the doubts that breast cancer would be more likely to occur in unhappy, dissatisfied, and worrying women.