CIRCADIAN REST-ACTIVITY DISTURBANCES IN SEASONAL AFFECTIVE-DISORDER

Background: Previous studies hypothesized that seasonal affective diso rder (SAD) was caused by a circadian rhythm abnormality. The purpose o f this study was to ascertain whether rest-activity rhythms were phase delayed, diminished in amplitude, or more poorly entrained to the 24- hour day. Method: Twenty healthy adult controls and 25 outpatients mee ting Rosenthal-National Institute of Mental Health criteria for SAD an d DSM-III-R criteria for major or bipolar depression with seasonal pat tern had their levels of activity recorded for 72 hours (weekdays) usi ng wrist-worn actigraphs. Results: Subjects with SAD had activity leve ls that were 11% lower than controls (P=.03), and their levels of acti vity were most attenuated during the first 2 hours after arising (P=.0 04). The relative amplitude of the circadian rhythm did nor differ bet ween groups. Patients with SAD were phase delayed by 50 minutes for th e entire period (P=.02). Analysis of each individual day indicated tha t patients were delayed by up to 70 minutes (P=.007). Interdaily stabi lity. an index of coupling between the rhythm and its zeitgeber was re duced in SAD (P=.01). Compared with controls, patients with SAD had be st-fit circadian periods chat were 92% more deviated from 24 hours (P= .007) and daily acrophase (time of the peak of the fit circadian rhyth m) times that were 110% more variable between days (P<.001). Conclusio ns: Patients with SAD have circadian rest-activity rhythms that are si gnificantly phase delayed and more poorly entrained to the 24-hour day .