Because nights are longer in winter, at night the brain's pineal body tends to secrete more melatonin, a hormone that helps people fall asleep. At daybreak, the production of melatonin gradually decreases and the body begins to perk up.
由於冬天黑夜長，腦部松果體在晚上會分泌「退黑激素」，這種荷爾蒙可以幫助人入睡；等天亮之後，退黑激素逐漸減少，人體也開始恢復精神。