Thermoregulatory effect in humans of suppressed endogenous melatonin by pre-sleep bright-light exposure in a cold environment

Keita Ishibashi, Satoshi Arikura, Tomoaki Kozaki, Shigekazu Higuchi, Akira Yasukouchi

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    26 Citations (Scopus)


    This study investigated the physiological function of suppressed melatonin through thermoregulation in a cold environment. Interactions between thermoregulation directly affected by exposure to a cold environment and indirectly affected by endogenous melatonin suppression by bright-light exposure were examined. Ten male subjects were exposed to two different illumination intensities (30 and 5000 lux) for 4.5h, and two different ambient temperatures (15 and 27°C) for 2h before sleep under dark and thermoneutral conditions. Salivary melatonin level was suppressed by bright light (p<0.001), although the ambient temperature condition had no significant effect on melatonin. During sleep, significant effects of pre-sleep exposure to a cold ambient temperature (p<0.001) and bright light (p<0.01) on rectal temperature (Tre) were observed. Pre-sleep, bright-light exposure led to an attenuated fall in Tre during sleep. Moreover, Tre dropped more precipitously after cold exposure than thermoneutral conditions (cold: -0.54±0.07°Ch; thermoneutral: -0.16±0.03°Ch; p<0.001). Pre-sleep, bright-light exposure delayed the nadir time of Tre under thermoneutral conditions (p<0.05), while cold exposure masked the circadian rhythm with a precipitous decrease in T re. A significant correlation between the Tre nadir and melatonin level (r-0.774, p<0.05) indicated that inter-individual differences with higher melatonin levels lead to a reduction in Tre after cold exposure. These results suggest that suppressed endogenous melatonin inhibits the downregulation of the body temperature set-point during sleep.

    Original languageEnglish
    Pages (from-to)782-806
    Number of pages25
    JournalChronobiology International
    Issue number4
    Publication statusPublished - May 2010

    All Science Journal Classification (ASJC) codes

    • Physiology
    • Physiology (medical)


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