Objective: The impact of hypnotic use on the association between insomnia and breast cancer risk remains unclear. This study examined whether insomnia increases the aforementioned risk and explored the effects of hypnotic use on this relationship. Materials and Methods: This retrospective cohort study was conducted using data retrieved from the Longitudinal Health Insurance Research Database 2010. In total, 11,021 patients with insomnia, who were categorized by hypnotic use and nonuse, were identified; 22,042 age-matched participants without insomnia were then randomly selected. Cox proportional hazards regression was used for the analyses. Results: The insomnia cohort had a higher risk of breast cancer than did the control cohort (adjusted hazard ratio [aHR] = 1.43; 95% confidence interval [CI] = 1.10-1.84). The aHR was 1.09 for insomniac with hypnotics use, 1.41 for insomniac without hypnotics use, and 0.71 for hypnotics users without insomnia (95% CIs = 0.71-1.68, 1.07-1.85, and 0.40-1.27) compared with those individuals without insomnia who did not use hypnotics. Conclusion: This nationwide population-based cohort study reveals that insomnia but not hypnotic use is associated with an increased risk of breast cancer.
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