The circadian clock in humans is controlled primarily by the suprachiasmatic nucleus (SCN) within the brain. The SCN is a group of cells that sit by the optic nerve and respond to light and other stimuli that come in from the eye. Hypothetically, caffeine could affect the SCN (and other tissues throughout the body) in various ways, depicted below.
Possible ways caffeine could affect circadian rhythm
One way is through increasing a cell’s levels of cyclic AMP (cAMP), which is often created inside a cell in response to a signal. This occurs for two reasons. First, caffeine blocks adenosine receptors that normally reduce cAMP levels. Second, caffeine binds phosphodiesterase enzymes that act to degrade cAMP.[1] When these enzymes are blocked, cAMP levels are raised.
It's also been shown that circadian rhythms within the SCN are regulated in part by the release of calcium ions during the stimulation of ryanodine receptors,[2] which caffeine also binds.[3]
References
- ^Choi OH, Shamim MT, Padgett WL, Daly JWCaffeine and theophylline analogues: correlation of behavioral effects with activity as adenosine receptor antagonists and as phosphodiesterase inhibitorsLife Sci.(1988)
- ^Ikeda M, Sugiyama T, Wallace CS, Gompf HS, Yoshioka T, Miyawaki A, Allen CNCircadian dynamics of cytosolic and nuclear Ca2+ in single suprachiasmatic nucleus neuronsNeuron.(2003 Apr 24)
- ^Kong H, Jones PP, Koop A, Zhang L, Duff HJ, Chen SRCaffeine induces Ca2+ release by reducing the threshold for luminal Ca2+ activation of the ryanodine receptorBiochem J.(2008 Sep 15)