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You can't put it on the calendar
If you experience a mood dip that accompanies the season's shorter days and longer nights, that could be due to a regular body process. "So many people experience a natural slowing of their thyroid in the winter, which allows them to 'hibernate' and conserve energy," says Kelly Brogan, MD, a Manhattan-based board-certified psychiatrist and author of A Mind of Your Own. What's different about having a thyroid condition like hypothyroidism (or, underactive thyroid) is that the low mood can come on at any time of year—and it doesn't predictably lift once the seasons change. Seeing your doctor may help get to the culprit, which he or she can determine by running a full thyroid panel with a simple blood test, says Aviva Romm, MD, author of The Adrenal Thyroid Revolution.