title: Circadian Rhythm and Sleep During Prolonged Antarctic Residence at Chinese Zhongshan Station.
abstract: OBJECTIVE
  Residence at Zhongshan Station (69°22'24″S, 76°22'40″E) for over 1 year exposes winter-over members to marked changes of light-dark cycle, ranging from the constant daylight of polar days to the constant darkness of polar nights, in addition to geographic and social isolation. This extreme photoperiodic environment may increase the risk of sleep disturbances and circadian desynchrony. The aim of this study was to investigate the circadian rhythm and sleep phase of Chinese winter-over expeditioners at Zhongshan Station.
  
  
  METHODS
  This study was conducted on 17 healthy male participants before departure from Shanghai and during residence at Zhongshan Station for 1 year (before winter, mid-winter, and end of winter). Sequential urine samples over 48 hours were obtained, 6-sulphatoxymelatonin in urine was assessed, and the circadian rhythm was analyzed by a cosine curve-fitting method. Participants' sleep parameters were obtained from wrist actigraphy and sleep logs. Morningness-Eveningness Questionnaire and Seasonal Pattern Assessment Questionnaire were completed.
  
  
  RESULTS
  The acrophase of 6-sulphatoxymelatonin rhythm, sleep onset, sleep offset, and mid-sleep time were delayed significantly (P < .05) in Antarctica relative to departure values. The subjects had greater eveningness preference (P < .05) in mid-winter in Antarctica. The Global Seasonality Score and the prevalence of subsyndromal seasonal affective disorder increased (P < .05) during winter.
  
  
  CONCLUSIONS
  Our results indicate that during polar nights Chinese expeditioners experienced the following problems: delayed circadian rhythm and sleep phase, later chronotype, and incidence of subsyndromal seasonal affective disorder. An appropriate combination of artificial bright light during dark winter months and a strict social schedule are recommended in a winter-over station in Antarctica.
authors.affiliation: Beijing Institute of Technology, Beijing, China (Mr Chen, Dr Song).
authors.forename: Nan
authors.initials: N
authors.lastname: Chen
authors.affiliation: Department of General Surgery, Beijing Jishuitan Hospital, Beijing, China (Dr Wu).
authors.forename: Quan
authors.initials: Q
authors.lastname: Wu
authors.affiliation: Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & School of Basic Medicine, Peking Union Medical College, Beijing, China (Ms Chen, Dr Xiong, Ms Xu).
authors.forename: Yanlei
authors.initials: Y
authors.lastname: Xiong
authors.affiliation: Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & School of Basic Medicine, Peking Union Medical College, Beijing, China (Ms Chen, Dr Xiong, Ms Xu).
authors.forename: Guang
authors.initials: G
authors.lastname: Chen
authors.affiliation: Beijing Institute of Technology, Beijing, China (Mr Chen, Dr Song).
authors.forename: Dandan
authors.initials: D
authors.lastname: Song
authors.affiliation: Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & School of Basic Medicine, Peking Union Medical College, Beijing, China (Ms Chen, Dr Xiong, Ms Xu). Electronic address: xuchengli@pumc.edu.cn.
authors.forename: Chengli
authors.initials: C
authors.lastname: Xu
mesh_terms: D000328:Adult; D000864:Antarctic Regions; D044466:Asian People; D002940:Circadian Rhythm / Q000502:physiology*; D003404:Creatinine / Q000652:urine; D000071251:Extreme Environments; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000652:urine; D008875:Middle Aged; D012621:Seasons; D012890:Sleep / Q000502:physiology*; D011795:Surveys and Questionnaires; D013997:Time Factors
chemical_list: C054513:6-sulfatoxymelatonin; D003404:Creatinine; D008550:Melatonin
keywords: Antarctica; circadian rhythm; light–dark cycle; sleep; winter-over