title: Is Heart Rate Variability Related to Season of Birth?
abstract: BACKGROUND
  Season of birth (SOB) has been found to be related to cardiovascular mortality, but the mechanisms are unclear. It is suggested that birth in winter is a protective factor for the circulatory system, and this should be able to be observed using heart rate variability (HRV) measurements. The phenomenon may have a sex difference and is likely to be modulated by climatic factors. This study focused on this problem and investigates healthy school-age children to minimize confounding factors.
  
  
  OBJECTIVE
  Birth in winter is protective to cardiovascular system via autonomic modulation. There is a gender difference in the relationship between SOB and autonomic activity. Climatic factors are the cause of SOB effects on autonomic system.
  
  
  METHODS
  A total of 381 healthy school-age children were recruited for this study. Their HRV profiles were measured once and climatic information related to their month of birth was gathered. The HRV profiles of the 2 sexes and 4 seasons of birth were compared. Correlation and regression analysis were performed to clarify the relationship between climatic factors and the HRV results.
  
  
  RESULTS
  Boys born in winter have higher high-frequency power (HF) but a lower ratio of low-frequency power to high-frequency power (LF/HF) than do males born in other seasons. This result is not found for girls. Age and the temperature of the SOB are predictive factors for HF among boys. The humidity of SOB is a predictive factor for normalized low-frequency power (LF%) and LF/HF among girls.
  
  
  CONCLUSIONS
  Season of birth is related to both parasympathetic and sympathetic activity among school-age children, especially boys. Temperature and humidity are potential causes of this SOB phenomenon.
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.|Department of Psychiatry, National Taiwan University Hospital, Yun-Lin Branch, Yunlin, Taiwan.|Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Wei-Lieh
authors.initials: WL
authors.lastname: Huang
authors.affiliation: Department of Pediatrics, Taipei City Hospital, Taipei, Taiwan.
authors.forename: Be-Tau
authors.initials: BT
authors.lastname: Hwang
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.|Sleep Research Center, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Chun-Ting
authors.initials: CT
authors.lastname: Lai
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.|Sleep Research Center, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Jia-Yi
authors.initials: JY
authors.lastname: Li
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.|Sleep Research Center, National Yang-Ming University, Taipei, Taiwan.|Brain Research Center, National Yang-Ming University, Taipei, Taiwan.|Department of Education and Research, Taipei City Hospital, Taipei, Taiwan.
authors.forename: Terry B J
authors.initials: TB
authors.lastname: Kuo
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.|Sleep Research Center, National Yang-Ming University, Taipei, Taiwan.|Brain Research Center, National Yang-Ming University, Taipei, Taiwan.|Department of Education and Research, Taipei City Hospital, Taipei, Taiwan.
authors.forename: Cheryl C H
authors.initials: CC
authors.lastname: Yang
mesh_terms: D002648:Child; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006813:Humidity; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology; D036801:Parturition / Q000502:physiology*; D012044:Regression Analysis; D012621:Seasons; D012737:Sex Factors; D013564:Sympathetic Nervous System / Q000502:physiology; D013696:Temperature