The effects of stopping melatonin production at night are unknown. Many animal studies, however, suggest that melatonin may slow down growth, particularly in breast cancer. Such studies have not been conducted in people, and the way melatonin relates to cancer risk in humans is not known. If melatonin production does affect cancer risk, we may expect several groups who are regularly exposed to bright light for long durations at night to have more cancer. Read the whole article here.