title: Sleep-related nighttime crying (yonaki) in Japan: a community-based study.
abstract: OBJECTIVE
  To examine factors associated with the phenomenon of yonaki, or sleep-related nighttime crying (SRNC), in Japanese children
  
  
  METHODS
  A cross-sectional design incorporating parental self-report was used to investigate relationships between developmental, psychologic, and constitutional/physiological factors in the incidence of SRNC. Participants were the parents of 170 infants, 174 toddlers, and 137 children at a well-infant clinic in Tokyo, Japan.
  
  
  RESULTS
  The lifetime incidence rates of SRNC were 18.8% (infants), 64.9% (toddlers), and 59.9% (children). At all ages, children were most likely to cosleep with their parents; however, infants with reported SRNC were found to cosleep more frequently, whereas infants without SRNC were more likely to sleep in separate, child-dedicated beds. Toddlers with frequent SRNC were more likely to have irregular bedtimes and to have nonparental day care than were those without SRNC. Preschoolers who typically slept 9.5 to 10.5 hours per night were less likely to report SRNC than were children with longer or shorter nighttime sleep durations. In all groups, children with frequent SRNC were more likely to suffer from chronic eczema, and toddlers and preschoolers with SRNC exhibited bruxism more frequently.
  
  
  CONCLUSIONS
  The traditional Japanese arrangement of cosleeping represents an environment in which parents are readily accessible to children during waking episodes. Physical proximity to the parents in infancy, but not at other ages, is associated with SRNC. The higher incidence of bruxism, chronic eczema, and day care use among children with frequent SRNC supports the hypothesis that nighttime anxiety may promote SRNC.
authors.affiliation: Department of Child Neurology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Tokyo, Japan. michio.fukumizu@umit.maine.edu
authors.forename: Michio
authors.initials: M
authors.lastname: Fukumizu
authors.forename: Makiko
authors.initials: M
authors.lastname: Kaga
authors.forename: Jun
authors.initials: J
authors.lastname: Kohyama
authors.forename: Marie J
authors.initials: MJ
authors.lastname: Hayes
mesh_terms: D002012:Bruxism / Q000150:complications; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003448:Crying; D003469:Culture; D003876:Dermatitis, Atopic / Q000150:complications; D005260:Female; D006801:Humans; D007223:Infant; D007564:Japan; D008297:Male; D010287:Parent-Child Relations; D016487:Parenting; D012111:Residence Characteristics; D012890:Sleep; D007319:Sleep Initiation and Maintenance Disorders / Q000150:complications / Q000208:ethnology; D011795:Surveys and Questionnaires