Researchers have found that drinking the equivalent
of a double espresso three hours before going to
sleep can turn back our body clock by around an
hour, a finding that could have important
implications for a range of sleep conditions.
Researchers from the MRC Laboratory of Molecular
Biology and the University of Colorado have, for the
first time, shown that caffeine directly affects the
body clock by delaying a rise in the level of the
hormone melatonin, the main sleep hormone released
by the body to make us feel sleepy.
To discover the effect caffeine has on the body
clock, the US scientists from the University of
Colorado studied five people to see when melatonin
starts to appear in saliva.
Each person lived in the lab for 49 days without a
clock or any knowledge of external light to tell
them if it was night or day.
They were then given caffeine, the equivalent of a
double espresso, or a placebo three hours before
they went to sleep and were exposed to dim or bright
light (the bright light acted as a control as it
also delays the human circadian clock) to find out
when the surge in melatonin occurred.
In those who were given the caffeine, their
melatonin levels rose around 40 minutes later than
those given the placebo.
To understand the mechanisms underpinning this
change, the UK based researchers at the MRC
Laboratory of Molecular Biology added caffeine to
human cells in the lab and found that it also
delayed their built-in circadian rhythm.
They found that caffeine affects adenosine receptors
which are found in all cells, and by reducing the
levels of this protein on the cell surface it
minimised the delay that caffeine would normally
Dr John O’Neill, joint lead researcher at the MRC
Laboratory of Molecular Biology, said: “The effect
of caffeine on sleep and wakefulness has been long
established, but its impact on the underlying body
clock has remained unknown. These findings could
have important implications for people with
circadian sleep disorders, where their normal 24
hour body clock doesn’t work properly, or even help
with getting over jet lag.
“Our findings also provide a more complete
explanation for why it’s harder for some people to
sleep if they’ve had a coffee in the evening –
because their internal clockwork thinks that they’re
an hour further west. By understanding the effect
caffeinated drinks have on our body clock, right
down to the level of individual cells, gives greater
insight into how we can influence our natural 24
hour cycle – for better or for worse.”
The body clock, or circadian rhythm, operates in
every single cell in the body, turning genes on and
off at different times of the day to allow us to
adapt to the external cycle of night and day.
Disruption of this, from shift work or regular jet
lag, can increase the risk of various cancers, heart
disease, type 2 diabetes and neurodegenerative
disorders such as Alzheimer’s.
For more information
Effects of caffeine on the human circadian clock in
vivo and in vitro
University of Colorado Boulder
MRC Laboratory of Molecular Biology