First you notice a loss of energy. You're not as chipper in the morning as you usually are. You find yourself snacking more often to try to jack yourself up, but you simply put on weight. You're not as enthusiastic as usual, and sometimes you're even feeling in the dumps. You don't have a history of depression--and you certainly don't have the signs of major depressive disorder--but it certainly feels as though you're down.
Interestingly, as many as two-thirds of all people who display signs of atypical depression evidence seasonality to their symptoms. This seasonal syndrome, known as SAD (seasonal affective disorder), affects roughly 10% of individuals in winter regions with reduced sunlight. My own experience with SAD began in Syracuse, NY, where I taught on the faculty of an academic department of psychiatry and ran a counseling program for medical and health science students. Quite a few of these students experienced symptoms of lowered energy and mood that were seasonally related.
To this day, even though I'm in sunnier suburban Chicago, I keep a phototherapy light in my office. This cranks out the light equivalent to a sunny day. Although I personally do not experience a full-blown SAD, I do experience the subclinical signs commonly known as winter blues. The daily dose of full sunlight has been helpful in starting my days--quite literally--on a bright note.
Studies in Finland find that the combination of exercise and light significantly improves seasonal mood declines. Interestingly, the authors found that even healthy individuals without winter blues benefit from the combination of light and exercise. Their work suggests that the light exposure has an even greater impact on mood than the exercise. My own experience is that light therapy is often sufficient for people who experience those winter blues; those who experience more profound depressive symptoms in winter can also benefit from a course of anti-depressant medication.
Mood affects decisions and can also impact concentration and other aspects of performance. Seasonal patterns of mood decline often go unnoticed. A careful investigation of your own mood patterns may help you take the steps to smooth your equity curve when the dark, dreary days of winter are upon us.