The Huffington Post examines the influence of weather and the outside environment on sleep.

As the days get shorter during fall and winter, we see less and less sunlight. This is especially true when you find yourself rising before sunrise or not leaving work until it’s dark outside.

Vitamin D is important for bones and muscles, and it’s also involved in serotonin production, which is important for many functions including our sleep-wake cycles. Our main source of vitamin D is sunlight, meaning when we don’t get sunlight we miss out. Research has shown that the lack of sunlight in winter may influence serotonin levels, providing a potential explanation for increased feelings of depression and fatigue as well as overeating.

Lower vitamin D levels have been associated with greater daytime drowsiness, and changes in light-dark cycles can also affect when your body releases melatonin making you feel tired earlier or later than usual.

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