同学前两天来海南，我问他睡得怎么样。他说，睡得比老家好多了。

今天发现一篇文章正好解释北方人来海南睡得好的原因：

那就是海南海拨低，氧气充足。

Resting easy: Oxygen promotes deep, restorative sleep

https://www.sciencedaily.com/releases/2018/12/181212134432.htm

1. Brandon E. Hauer, Biruk Negash, Kingsley Chan, Wesley Vuong, Frederick Colbourne, Silvia Pagliardini, Clayton T. Dickson. Hyperoxia enhances slow-wave forebrain states in urethane-anesthetized and naturally sleeping rats. Journal of Neurophysiology, 2018; 120 (4): 1505 DOI: 10.1152/jn.00373.2018