Melatonin is a hormone secreted by the pineal gland in the brain. It helps regulate other hormones and maintains the body’s circadian rhythm. The circadian rhythm is an internal 24-hour “clock” that plays a critical role in when we fall asleep and when we wake up. When it is dark, your body produces more melatonin; when it is light, the production of melatonin drops. Being exposed to bright lights in the evening or too little light during the day can disrupt the body’s normal melatonin cycles. For example, jet lag, shift work, and poor vision can disrupt melatonin cycles.
Melatonin also helps control the timing and release of female reproductive hormones. It helps determine when a woman starts to menstruate, the frequency and duration of menstrual cycles, and when a woman stops menstruating (menopause).
Some researchers also believe that melatonin levels may be related to aging. For example, young children have the highest levels of nighttime melatonin. Researchers believe these levels drop as we age. Some people think lower levels of melatonin may explain why some older adults have sleep problems and tend to go to bed and wake up earlier than when they were younger. However, newer research calls this theory into question.
Melatonin has strong antioxidant effects. Preliminary evidence suggests that it may help strengthen the immune system.