Sleep characteristics and risk of ovarian cancer among postmenopausal women.

Several studies have assessed the relationship between sleep duration and ovarian cancer risk, but the results are conflicting. Importantly, no studies addressed the relationship between sleep disturbance or sleep quality and ovarian cancer incidence. Moreover, few studies have examined the relationships between sleep measures and subtypes of ovarian cancer. This study included 109,024 postmenopausal women aged 50-79 from the Women's Health Initiative (WHI) during 1993-1998 and followed through 2018. The Cox proportional hazards model was used to estimate adjusted hazard ratios for the associations between sleep habits and the incidence of ovarian cancer and its subtypes. No association was observed between sleep duration, sleep quality, sleep disturbance, or insomnia and risk of overall ovarian cancer, serous/non-serous or Type I/Type II ovarian cancer subtype. However, compared with women with average sleep quality, women with restful or very restful sleep quality had a significantly lower risk of invasive serous subtype (HR: 0.73, 95% CI: 0.60-0.90) while insomnia was associated with a higher risk of invasive serous subtype (HR: 1.36, 95% CI: 1.12-1.66). Associations with insomnia differed significantly by serous and non-serous subtypes, and Type I and Type II subtypes (Pheterogeneity=0.001 and Pheterogeneity<0.001, respectively). This study provides no evidence on association between sleep habits and overall ovarian cancer risk among postmenopausal women. However, restful or very restful sleep quality was associated with a lower risk of invasive serous ovarian cancer, and insomnia was associated with a higher risk of invasive serous ovarian cancer. Associations with insomnia differed by subtypes.