Ask The Doctor: Summer Tips To Prevent Winter SAD
By John Greden, MD | esperanza magazine: 
Make no mistake: seasonal affective disorder (SAD) is real. SAD is best understood as a cyclical, seasonal, circadian pattern that affects people with major depressive disorder or bipolar illness who have an underlying genetic vulnerability to diminishing sunlight.
Make no mistake: seasonal affective disorder (SAD) is real. SAD is best understood as a cyclical, seasonal, circadian pattern that affects people with major depressive disorder or bipolar illness who have an underlying genetic vulnerability to diminishing sunlight.
In fact, the current diagnostic label is depression “with seasonal pattern,” but SAD is a more familiar reference.
Light absorbed through the eyes influences brain levels of serotonin and melatonin, which govern mood, sleep, and daily rhythms of alertness, energy, and appetite. As the seasons change and the days become shorter (and grayer), SAD symptoms begin to affect approximately five percent of the total population. In parts of the globe with little sunlight, as many as 20 percent may be affected.
SAD symptoms typically emerge around September or October in the northern hemisphere. Every several hundred miles further away from the equator translates to an earlier week of onset.