A reader asks:

I understand that only a small percentage of the population exhibits symptoms clinically significant enough to be diagnosed as being seasonal affective disorder (SAD). However, to what extent would you expect SAD-like symptoms to affect the rest of the population? In northern latitudes, does it appear that the majority show changes in mood and behavior similar but not as severe as those for SAD?


The number of people with “winter doldrums” or subsyndromal SAD is at least three times higher than the number with full-fledged SAD. The difference between the two groups is subtle, not obvious. Doldrums sufferers experience the same range of winter symptoms, including depressed mood, but short of a major depressive episode. Broadly speaking, they can plow through winter with effort without becoming overwhelmed and seriously dysfunctional. The months of symptom onset and springtime remission are the same as for SAD. Doldrums sufferers also respond well to light therapy, and usually they need the same lighting regimen as for SAD: the same light intensity, exposure duration and time of day of treatment. CET helps people differentiate SAD from subsyndromal SAD in its Automated Personalized Inventory for Depression and SAD (AutoPIDS at www.cet.org), and offers personalized start-up guidelines for treatment in its Automated Morningness-Eveningness Questionnaire (AutoMEQ). We do not believe that a majority of people show subsyndromal SAD; the proportion is probably closer to 30% in middle-to-northern latitudes of the U.S. and southern Canada.