‘Drinking coffee late disrupts body clock’
The body clock, or circadian rhythm, operates in every single cell in the body, turning genes on and off at different times to allow us to adapt to the external cycle of night and day. The hormone melatonin, which makes people feel sleepy, is released upon certain triggers, such as the dimming of light.
Disruption of the rhythm, through shift work, jet lag or sleep disorders, can lead to a range of sleep conditions, with knock-on effects such as heart disease, type 2 diabetes, Alzheimer’s disease and certain psychiatric conditions.
It now appears that drinking the equivalent of a double espresso three hours before going to sleep can turn back the clock by an hour, by delaying a rise in the level of the hormone melatonin.
The finding could have important implications for a range of sleep conditions at a time when more than 25 per cent of population are not getting enough sleep, while nearly 10 per cent experience chronic insomnia.
The report, published in Science Translational Medicine, describes an experiment in which five people were invited to live in a lab for 49 days without a clock or any knowledge of external light to tell them if it was night or day.
Participants were exposed to bright or dim light; bright light, like caffeine, is known to be a stimulus that lengthens the circadian phase.
The participants were given either caffeine – the equivalent of a double espresso – or a placebo three hours before going to sleep. Their saliva was then tested three hours later to see how much melatonin had been produced.