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  • Title: Preliminary studies on the immediate phase-shifting effects of light and exercise on the human circadian clock.
    Author: Van Cauter E, Sturis J, Byrne MM, Blackman JD, Scherberg NH, Leproult R, Refetoff S, Van Reeth O.
    Journal: J Biol Rhythms; 1993; 8 Suppl():S99-108. PubMed ID: 8274769.
    Abstract:
    The aim of the present research was to determine the magnitude and direction of immediate phase shifts of human rhythms following a single exposure to a 3-hr pulse of bright light or physical activity. The pulse of light or activity was presented under "constant-routine" conditions, and measurements of the resultant phase shifts were performed under the same constant-routine conditions on the first day following pulse presentation. Four overt rhythms that are strongly dependent on circadian timing--namely, the rhythms of plasma cortisol, plasma thyroid-stimulating hormone (TSH), plasma melatonin, and body temperature--were monitored. The analysis of the TSH profiles indicated that exposure to light at about the time of the minimum of body temperature resulted in phase advances averaging less than 1 hr in magnitude. Exposure to light approximately 3 hr before the time of the minimum of body temperature resulted in phase delays of 1-2 hr. Preliminary analyses of the melatonin profiles have confirmed these observations. Our findings regarding the effects of exercise are still inconclusive.
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