Exposure to long summer days affects the human melatonin and cortisol rhythms

Brain Res. 1997 Jun 6;759(1):166-70. doi: 10.1016/s0006-8993(97)00358-2.


Exposure of 8 human subjects in summer to a natural 16 h bright light photoperiod phase advanced the morning salivary melatonin decline and cortisol rise and shortened the nocturnal melatonin signal by 2 h relative to the winter patterns of the same subjects followed under a combined artificial and natural light 16 h photoperiod. The data suggest that summer days experienced from sunrise till sunset and not winter days with a combined artificial and natural light long photoperiod evoke a true long day response of the human circadian system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Circadian Rhythm*
  • Female
  • Humans
  • Hydrocortisone / metabolism*
  • Lighting
  • Male
  • Melatonin / metabolism*
  • Photoperiod*
  • Saliva / metabolism
  • Saliva / radiation effects
  • Seasons*
  • Sunlight


  • Melatonin
  • Hydrocortisone