Cancer
In a prospective study of 23,995 Japanese women, shorter sleep duration, specifically six hours or less per night, was associated with a higher risk of breast cancer when compared with women who slept seven hours per night. Researchers suggested that melatonin, which is secreted mainly from the pineal gland, is the key factor in this link between sleep and cancer. Shorter sleep results in a shorter duration of nocturnal melatonin secretion and lower melatonin levels have been associated with an increased risk of breast cancer.