（7）睡眠覚醒リズムと時計遺伝子，ホルモン

抄録

In recent years, rhythmic fluctuations in life, organized by biological clocks, have been found to maintain health and prevent aging and certain diseases. Circadian signals are transmitted from the central clock in the suprachiasmatic nuclei located in the hypothalamus to the local clocks in the brain and most peripheral tissues, which coordinate the function of nerves, hormone secretion, and sleep-wake rhythms. Clock genes regulate the biological clock, and if their expression level decreases, the movement of the clock deteriorates, which harms health. Humans have an internal cycle of more than 24 h, and the appropriate timing is maintained according to external daily stimuli, such as morning light. Local clocks in the peripheral tissues have a strong direct response to external stimuli of stress, exercise, and/or food, that are independent of the central clock. Therefore, light exposure, diet, and exercise at the appropriate times of the day lead to a healthy lifestyle. Melatonin, a sleep hormone, begins to be secreted at night due to morning light, increases at night, and decreases at dawn, which is disrupted by light exposure at night; therefore, it is important to limit light exposure at night to maintain sleep.