Some studies also suggest that the light cycle may regulate the production of blood stem cells from the bone marrow. That could potentially lead to more mutated cells that can trigger cancer. Studies in shift workers found that less melatonin may also lead to lower levels of important chemicals the body uses to repair DNA. In winter months when the days are shorter, melatonin levels may peak earlier or later in the day, which can lead to some of the mood changes linked to SAD. As more light creeps in during the morning, the levels of the hormone start dropping again.
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Normally, people produce more melatonin toward the evening, as the body gets ready for sleep. There is also intriguing evidence finding that people who work at night and don’t get exposed to daylight may produce less melatonin, a hormone that is dependent on light. People who consistently work night shifts, for example, tend to be heavier than people who don’t. That can have domino effects on nearly everything: how we break down energy from food, how strong our immune systems are and the vast array of brain chemicals and other substances that contribute to mood, weight, energy and more. Messing up the normal light and dark cycles by sleeping during the day and being awake at night, under artificial light, can disrupt the body’s metabolism. Studies of shift workers also support the possible role that exposure to sunlight has on mood. TIME Health Get the latest health and science news, plus: burning questions and expert tips.
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