Phase-Shifting Effect of Light and Exercise on the Human Circadian Clock
Annual rept. 1 Mar 1991-28 Feb 1993
CHICAGO UNIV IL DEPT OF MEDICINE
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The aim of the present study was to determine the magnitude and direction of immediate phaseshifts of human rhythms following a single exposure to a 3-hour pulse of bright light or physical activity. The pulse of light or activity was presented under constant routine conditions and measurement of the resultant phase-shifts were performed under the same constant routine conditions on the first day following pulse presentation. Four oven rhythms which are strongly dependent on circadian timing, i.e., the rhythms of plasma cortisol, plasma TSH, plasma melatonin and body temperature, were monitored. Based on the analysis of the TSH profiles, our findings indicate that exposure to light around the time of the minimum of body temperature results in phase-advances averaging less than one hour in magnitude. Exposure to light approximately 3 hours before the time of the minimum of body temperature results in 1-2 hour phase delays. Preliminary analyses of the melatonin profiles confirm these observations. Our findings regarding the effects of exercise are still inconclusive.
- Anatomy and Physiology