We thank Dr Nagai and colleagues for their interest in our study and for comments on the correlation between long sleep duration and intracerebral hemorrhage (ICH). They suggested that arterial stiffness and blood pressure variability could be pivotal moderators for the relationship between long sleep duration and ICH risk. Their comments give us an opportunity to consider the relationship between long sleep duration and the risk of ICH from a different point of view. We would reply to their comments as follows. Arterial stiffness associated with long sleep duration might be a possible mechanism to increase risk of ICH. Previous studies suggested that increased sympathetic activity related to sleep fragmentation might lead to arterial stiffening in long sleep duration patients [1,2]. However, sleep fragmentation was not associated with long sleep duration in our study. Therefore, we find no clues that arterial stiffness related to increased activity of the sympathetic nervous system might contribute to the increased risk of ICH [3]. Blood pressure variability could be a moderator for the correlation between long sleep duration and increased risk of ICH [4,5]. Unfortunately we do not have data regarding blood pressure variability in our study subjects to discuss the issue. Future studies would be required to clarify the suggested relationship. Disclosure of conflicts of interest
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