Health
Ancient people said: “If you live according to the Qi energy of the Heaven and Earth, you will live as long as Heaven and Earth live” ("Yellow Emperor's Inner Canon"). The Earth rotates around the Sun, the Moon revolves around the Earth, the high tide of the sea is followed by ebb, night comes after day, winter gives way to spring as spring to summer. It is clear, that in nature everything moves by it's own rhythm.
From a physiological point of view, the human is a highly organized, multi-cellular organism with strong life-support systems. The human body lives by it's own biological rhythm. We are awake during the day, because our blood is filled with 'daytime hormones' that support emotional and physical activity. In the evening, preceding nightfall the blood receives the 'night hormone' melatonin. This is an amazing substance that is produced only by epiphysis at night and it is released into the blood according to the time of the night. In some cases, seniors suffer from insomnia due to the lack of melatonin secretion. Melatonin medications are often used as hypnotics.