Seasonal Affective Disorder
Seasonal Affective Disorder (now called Major Depressive Disorder with a Seasonal Pattern) affects 66 million US Americans, 10 million of which have severe symptoms that get in the way of functioning on a day to day basis.
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As the days get colder, darker and shorter our bodies produce less serotonin, melatonin and Vitamin D that can throw off our circadian rhythms, sleep-waking cycles and mood. We often cope with less exercise, more alcohol and sugar/carbs during the winter months that can exacerbate our symptoms of irritability, fatigue, lack of libido, difficulty concentrating and overall lower mood/energy.
Thankfully, there are treatments including light therapy (10,000 lux light boxes) we can view for 30-90 minutes a day, often in the morning and/or spread out throughout the day. Simple solutions like moving our desk/chair near a window and going outside daily can help too. Of course the more we're able to have regular exercise, good nutrition, adequate sleep and social support the better we can cope with mood and anxiety shifts when they occur.