We all know that drinking caffeinated drinks before bed can disrupt sleep. But for the first time research suggests that your evening double espresso delays the internal circadian clock that tells us when to get ready for sleep and when to prepare to wake up.
A new study led by the University of Colorado Boulder and the Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England shows that the internal clocks in human cells can be impacted by caffeine intake. According to Professor Kenneth Wright “this is the first study to show that caffeine, the most widely used psychoactive drug in the world, has an influence on the human circadian clock.”
In the study, they compared what happened to people’s body clocks when they were exposed to caffeine three hours before bedtime to what happened when people were exposed to bright light at nighttime – which is already known to delay the body clock.
Researchers measured saliva levels of melatonin, which is a key hormone involved in regulating the body clock. It showed that drinking caffeine at night delays the body clock by 40 minutes. But it was found that the effect of caffeine is about half of what we see with light. The study showed that bright light alone and bright light combined with caffeine induced circadian phase delays in the test subjects of about 85 minutes and 105 minutes respectively.
The research suggests that not only will caffeine keep you awake longer at night but it could also push you into you into a whole new time zone.
While this may not be everyone’s cup of tea, these new results could benefit travellers. If the intake of caffeine is timed properly, it could help shift the circadian clocks of those flying west over multiple time zones.
The findings suggested that chronic use of caffeine to stay up late will train the body clock to be delayed and will make it difficult for people to get up a the usual time without suffering jetlag type symptoms.
According to behavioural neurologist, Charmane Eastman of Rush University Chicago, “The study shows that caffeine can also make your internal circadian body clock later, which could make it difficult to fall asleep the next night even if you don’t take caffeine again”
So it seems that caffeine is not only keeping you awake but is also pushing your internal clock later so you want to go to sleep later.
However the research does not say anything about how coffee consumption in the morning or any other time during the day may affect the body’s internal clock so findings need to be confirmed. If they can be though, then removing coffee from your diet or just having one cup in the morning might help you achieve earlier bedtimes and wake times.
1. University of Colorado at Boulder (2015) Science Daily Website. Accessed on 30 September 2015 at http://www.sciencedaily.com/releases/2015/09/150916161833.ht
2. 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. Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 2015; 7 (305): 305ra146 DOI: 10.1126/scitranslmed.aac5125
3. Sallen, A (2015) ABC News Website. Accessed on 30 September 2015 at
4. Williams, R (2015) The Scientist Magazine Online. Accessed on 1 October 2015