Have you ever thought about why people sleep at night? When night falls, what makes us maintain this day after day, year after year “sleep-wake” life pattern? It turns out that there is a gland in our brain called the pineal gland, which can secrete and release a neuroendocrine hormone called “melatonin”. The secretion of melatonin begins to increase at nightfall and reaches its peak at midnight. Due to the sleep-promoting effect of melatonin, people enter into sweet dreams. As dawn approaches, melatonin secretion decreases and people wake up from their sleep. Its secretion is related to the intensity of light, and melatonin secretion is considerably more in the dark than in the light, so it is related to regulating people’s sleep, which is why it is easier to fall asleep in the dark. We all basically have this life experience, that is, you rarely hear children say that they can not sleep, but often hear the elderly complain about not being able to sleep and wake up early, what is the reason for this? In fact, it is because the synthesis of melatonin, which controls our sleep, is age-related. Generally in the newborn baby body can only detect a very small amount of melatonin, until 3 months of age, the secretion increased, and showed a more obvious circadian rhythm phenomenon. The secretion of the highest amount of young children, adolescence secretion slightly decreased, and then gradually decline with age, to the elderly secretion gradually decreased, the peak secretion disappeared. Therefore, older people are more likely to have sleep disorders. The circadian fluctuations of melatonin show a 24-hour rhythm, influenced by the circadian light and dark cycle, light is transmitted from the retina via the superior cervical sympathetic ganglion and the suprachiasmatic nucleus (SCN), and melatonin synthesis and release increase at night. During the daytime, the retina senses bright light, which inhibits the activity of the SCN through the hypothalamus, and melatonin synthesis and secretion are reduced. The biological role of melatonin is very broad, and the mechanism of its hypnotic effect is not clear. There are several theories: 1, melatonin directly plays a mandatory sedative-hypnotic effect; 2, melatonin acts on the supraoptic nucleus and other parts of the nucleus, by opening the “gate” of sleep and make people fall asleep easily; 3, melatonin can also induce sleep by lowering the body temperature and clearing the free radicals in the brain. Science Tips: If you are working or thinking at home, then go out in the yard and think in the sun; if you are on vacation, plan some outdoor activities to feel the sun; if you wake up, please immediately open the curtains or blinds to let the sun shine in; if you are still wearing sunglasses in the morning and evening, please take them off and get some sunshine.