Editors' ChoiceCircadian Biology

Your daily drug resets your clock

Sci. Signal.  22 Sep 2015:
Vol. 8, Issue 395, pp. ec275
DOI: 10.1126/scisignal.aad4851

Your morning cup of coffee may be shifting your circadian clock. Burke et al. show that caffeine—widely available, legal, and psychoactive—inserts a delay into the ~24-hour metabolic rhythm that keeps your body running in time with the world. Five people were kept under highly controlled conditions for 49 days. Before bedtime, they were given various treatments: either a double-espresso caffeine dose, exposure to bright or dim light, or a placebo. The caffeine delayed their internal clock by 40 min, a shift about half as long as bright light, a stimulus known to robustly lengthen the circadian phase. Caffeine has several molecular targets, including ryanodine receptors and adenosine receptors. Experiment with cultured cells expressing a circadian-regulated reporter gene showed that the circadian rhythm-altering effects were mediated by caffeine antagonizing type I adenosine receptors, which increased the intracellular messenger molecule cyclic AMP. Not only do these results reinforce the common advice to avoid caffeine in the evening, but they also raise the intriguing possibility that caffeine may be useful for resetting the circadian clock to treat jet lag induced by international time zone travel.

T. M. Burke, R. R. Markwald, A. W. McHill, E. D. Chinoy, J. A. Snider, S. C. Bessman, C. M. Jung, J. S. O’Neill, K. P. Wright Jr., Effects of caffeine on the human circadian clock in vivo and in vitro. Sci. Transl. Med. 7, 305ra146 (2015). [Abstract]

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