ObjectivesEmerging evidence indicates that sleep duration is associated with health outcomes. However, the relationship of sleep duration with long-term health is unclear. This study was designed to determine the relationship of sleep duration with mortality as a parameter for long-term health in a large prospective cohort study in Korea.MethodsThe study population included 13 164 participants aged over 20 years from the Korean Multi-center Cancer Cohort study. Information on sleep duration was obtained through a structured questionnaire interview. The hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality were estimated using a Cox regression model. The non-linear relationship between sleep duration and mortality was examined non-parametrically using restricted cubic splines.ResultsThe HRs for all-cause mortality showed a U-shape, with the lowest point at sleep duration of 7 to 8 hours. There was an increased risk of death among persons with sleep duration of ≤5 hours (HR, 1.21; 95% CI, 1.03 to 1.41) and of ≥10 hours (HR, 1.36; 95% CI, 1.07 to 1.72). In stratified analysis, this relationship of HR was seen in women and in participants aged ≥60 years. Risk of cardiovascular disease-specific mortality was associated with a sleep duration of ≤5 hours (HR, 1.40; 95% CI, 1.02 to 1.93). Risk of death from respiratory disease was associated with sleep duration at both extremes (≤5 and ≥10 hours).ConclusionsSleep durations of 7 to 8 hours may be recommended to the public for a general healthy lifestyle in Korea.

IntroductionDiabetes mellitus (DM) is an important risk factor for endocrine cancers; however, the association with thyroid cancer is not clear. We performed a systematic review and meta-analysis to clarify the association between thyroid cancer and DM.MethodsWe searched MEDLINE, PUBMED and EMBASE databases through July 2012, using search terms related to diabetes mellitus, cancer, and thyroid cancer. We conducted a meta-analysis of the risk of incidence of thyroid cancer from pre-existing diabetes. Of 2,123 titles initially identified, sixteen articles met our inclusion criteria. An additional article was identified from a bibliography. Totally, 14 cohort and 3 case-control studies were selected for the meta-analysis. The risks were estimated using random-effects model and sensitivity test for the studies which reported risk estimates and used different definition of DM.ResultsCompared with individuals without DM, the patients with DM were at 1.34-fold higher risk for thyroid cancer (95% CI 1.11–1.63). However, there was heterogeneity in the results (p<0.0001). Sensitivity tests and studies judged to be high quality did not show heterogeneity and DM was associated with higher risk for thyroid cancer in these sub-analyses (both of RRs = 1.18, 95% CIs 1.08–1.28). DM was associated with a 1.38-fold increased risk of thyroid cancer in women (95% CI 1.13–1.67) after sensitivity test. Risk of thyroid cancer in men did not remain significant (RR 1.11, 95% CI 0.80–1.53).ConclusionsCompared with their non-diabetic counterparts, women with pre-existing DM have an increased risk of thyroid cancer.

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BackgroundBreast and ovarian cancers are predominant female cancers with increasing prevalence. The purpose of this study was to estimate the population attributable risks (PARs) of breast and ovarian cancer occurrence based on the relative risks (RRs) of modifiable reproductive factors and population-specific exposure prevalence.MethodsThe PAR was calculated by using the 1990 standardized prevalence rates, the 2010 national cancer incidence with a 20 year lag period, the meta-analyzed RRs from studies conducted in the Korean population for breast cancer, and the meta-analyzed RRs from a Korean epithelial ovarian cancer study and a prior meta-analysis, and ovarian cancer cohort results up to 2012. For oral contraceptive and hormone replacement therapy use, we did not consider lag period.ResultsThe summary PARs for modifiable reproductive factors were 16.7 % (95 % CI 15.8–17.6) for breast cancer (2404 cases) and 81.9 % (95 % CI 55.0–100.0) for ovarian cancer (1579 cases). The modifiable reproductive factors included pregnancy/age at first birth (8.0 %), total period of breastfeeding (3.1 %), oral contraceptive use (5.3 %), and hormone replacement therapy use (0.3 %) for breast cancer and included breastfeeding experience (2.9 %), pregnancy (1.2 %), tubal ligation (24.5 %), and oral contraceptive use (53.3 %) for ovarian cancer.ConclusionsDespite inherent uncertainties in the risk factors for breast and ovarian cancers, we suggest that appropriate long-term control of modifiable reproductive factors could reduce breast and ovarian cancer incidences and their related burdens by 16.7 % and 81.9 %, respectively.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-2040-0) contains supplementary material, which is available to authorized users.

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The long-term follow-up results of this study suggest that RAI treatment for patients with thyroid cancer may not increase the risk or recurrence of breast cancer.