title: Suppression of vagal cardiac modulation by blue light in healthy subjects.
abstract: BACKGROUND
  In the contemporary life environments, our body is increasingly exposed to various sources of colored light, which may affect our physiological functions as non-image-forming effects. We examined the impacts of colored lights on the autonomic functions by the analysis of heart rate variability (HRV).
  
  
  METHODS
  A lighting device consisting of four organic light-emitting diode (OLED) modules (55 × 55 mm2) with adjustable red-green-blue color was secured 24 cm above the eyes of subject lying supine in a light-shielded laboratory. Following a 15-min supine rest, electrocardiogram and respiration were measured continuously during 3-min darkness, 6-min colored OLED illumination, and 3-min darkness under paced breathing (15 breath/min). The measurements were repeated at a 45-min interval for red, green, and blue lights with melanopsin-stimulating photon flux density (MSPFD) of 0.00, 0.10, and 0.20 μmol/m2/s, respectively, in 12 healthy subjects (23 ± 2 years, two females). Additionally, the effects of blue lights with 0.20, 0.10, and 0.04 μmol/m2/s MSPFD were examined in four healthy subjects (25-39 years, two females). HRV was analyzed for low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.20-0.30 Hz) power and LF-to-HF ratio (LF/HF).
  
  
  RESULTS
  Compared to darkness before lighting, HF power decreased (P < 0.001) and LF/HF increased (P = 0.024) during lighting on average of all color lights, whereas HF power showed a greater decrease with blue light than with red and green lights (P < 0.05 for both). The decrease in HF power lasted even during darkness after lighting (P < 0.001). HF power decreased with blue light with 0.20 μmol/m2/s MSPFD (P < 0.001) but not with that with 0.10 or 0.04 μmol/m2/s (P = 0.1 and 0.9, respectively).
  
  
  CONCLUSIONS
  Vagal cardiac modulation is suppressed by OLED blue light in healthy subjects most likely through melanopsin-dependent non-image-forming effect.
authors.affiliation: Department of Medical Education, Nagoya City University Graduate School of Medical Sciences, Kawasumi 1 Mizuho-cho Mizuho-ku, Nagoya, 467-8601, Japan.
authors.forename: Emi
authors.initials: E
authors.lastname: Yuda
authors.affiliation: Department of Medical Education, Nagoya City University Graduate School of Medical Sciences, Kawasumi 1 Mizuho-cho Mizuho-ku, Nagoya, 467-8601, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Ogasawara
authors.affiliation: Department of Medical Education, Nagoya City University Graduate School of Medical Sciences, Kawasumi 1 Mizuho-cho Mizuho-ku, Nagoya, 467-8601, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yoshida
authors.affiliation: Department of Medical Education, Nagoya City University Graduate School of Medical Sciences, Kawasumi 1 Mizuho-cho Mizuho-ku, Nagoya, 467-8601, Japan. hayano@med.nagoya-cu.ac.jp.
authors.forename: Junichiro
authors.initials: J
authors.lastname: Hayano
mesh_terms: D000328:Adult; D003116:Color; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000528:radiation effects*; D006801:Humans; D008027:Light; D008297:Male; D012143:Respiratory Physiological Phenomena; D014630:Vagus Nerve / Q000528:radiation effects*; D055815:Young Adult
keywords: Blue light; Heart rate variability; Intrinsically photosensitive retinal ganglion cell; Melanopsin; Non-image-forming vision; Organic light-emitting diode