title: Circadian rest-activity disturbances in seasonal affective disorder.
abstract: BACKGROUND
  Previous studies hypothesized that seasonal affective disorder (SAD) was caused by a circadian rhythm abnormality. The purpose of this study was to ascertain whether rest-activity rhythms were phase delayed, diminished in amplitude, or more poorly entrained to the 24-hour day.
  
  
  METHODS
  Twenty healthy adult controls and 25 outpatients meeting Rosenthal-National Institute of Mental Health criteria for SAD and DSM-III-R criteria for major or bipolar depression with seasonal pattern had their levels of activity recorded for 72 hours (weekdays) using wrist-worn actigraphs.
  
  
  RESULTS
  Subjects with SAD had activity levels that were 11% lower than controls (P = .03), and their levels of activity were most attenuated during the first 2 hours after arising (P = .004). The relative amplitude of the circadian rhythm did not differ between groups. Patients with SAD were phase delayed by 50 minutes for the entire period (P = .02). Analysis of each individual day indicated that patients were delayed by up to 70 minutes (P = .007). Interdaily stability, an index of coupling between the rhythm and its zeitigeber was reduced in SAD (P = .01). Compared with controls, patients with SAD had best-fit circadian periods that were 92% more deviated from 24 hours (P = .007) and daily acrophase (time of the peak of the fit circadian rhythm) times that were 110% more variable between days (P < .001).
  
  
  CONCLUSIONS
  Patients with SAD have circadian rest-activity rhythms that are significantly phase delayed and more poorly entrained to the 24-hour day.
authors.affiliation: Department of Psychiatry, Harvard Medical School, Boston, Mass, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Teicher
authors.forename: C A
authors.initials: CA
authors.lastname: Glod
authors.forename: E
authors.initials: E
authors.lastname: Magnus
authors.forename: D
authors.initials: D
authors.lastname: Harper
authors.forename: G
authors.initials: G
authors.lastname: Benson
authors.forename: K
authors.initials: K
authors.lastname: Krueger
authors.forename: C E
authors.initials: CE
authors.lastname: McGreenery
mesh_terms: D000204:Activity Cycles; D000293:Adolescent; D000328:Adult; D000368:Aged; D000553:Ambulatory Care; D002909:Chronobiology Phenomena; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D008124:Locomotion; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D012146:Rest; D016574:Seasonal Affective Disorder / Q000175:diagnosis* / Q000523:psychology