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Phoenix666 writes:

Do you suffer from SAD (Seasonal Affective Disorder)? A new theory explains why:

When dawn comes later in the winter, the end of melatonin secretion drifts later, says Kripke. From animal studies, it appears that high melatonin levels just after the time an animal wakes up strongly suppress the making of active thyroid hormone—and lowering thyroid levels in the brain can cause changes in mood, appetite, and energy. For instance, thyroid hormone is known to influence serotonin, a neurotransmitter that regulates mood. Several studies have shown that levels of brain serotonin in humans are at their lowest in the winter and highest in the summer. In 2016, scientists in Canada discovered that people with severe SAD show greater seasonal changes in a protein that terminates the action of serotonin than others with no or less severe symptoms, suggesting that the condition and the neurotransmitter are linked.

It's possible that many of these mechanisms are at work, even if the precise relationships haven't been fully teased apart yet. But regardless of what causes winter depression, bright light—particularly when delivered in the early morning—seems to reverse the symptoms.

Bright, full spectrum lights do the trick.

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