A reader asks:

Do people who suffer from SAD usually have circadian rhythms that are somewhat “off”? I am just curious since you have said that the best antidepressant effect comes from resetting the internal clock earlier. Do people who have “normal” circadian rhythms tend to not get SAD?


On the one hand, we could say that the circadian rhythms are “off” during winter depression, in the sense that relief is obtained by shifting the rhythms earlier. Furthermore, come springtime, it appears that the internal clock spontaneously shifts earlier, at least for people who are “evening types” in winter. (To check your chronotype, take the Automated Morningness-Eveningness Questionnaire ) On the other hand, SAD patients can be morning types, intermediate types or evening types — the same distribution that exists in the healthy, non-depressed population. What appears different about people with SAD is their mood lift when light therapy shifts the internal clock earlier, regardless of chronotype.