We thank Drs. Erren and Reiter for their thoughtful comments.1 We agree that a more comprehensive assessment of lifetime sleep patterns would be necessary to better understand the interrelationships between sleep, melatonin and risk of breast cancer. We acknowledged in our paper and we emphasized again that our assessment of sleep hours was very crude, was based on self-reported estimate at one time point, and that random misclassification of this exposure variable likely contributed to our null findings.2 However, we still believe our analysis was well-justified given our previous findings on sleep duration and risk of breast cancer as well as sleep duration and melatonin levels.3
The recent null findings on sleep and breast cancer risk from a case-control study in Western Australia which carefully investigated multiple metrics of sleep duration (cumulative, average, duration, and peak) as well as sleep quality4,5 highlights the complexity of this research question. This Australian team showed that while their questions on sleep quality were reasonably reliable, there was poor agreement between self-reported sleep and objective measures of sleep quality.6, 7 We hope our results will stimulate new interest to develop questionnaire assessment tools that can be used in prospective cohort studies as well as case-control studies so that the relationship between sleep and risk of breast cancer and other health endpoints will be identified.
References
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