Many of us are reliant on coffee for a much-needed boost first thing in the morning, but it if you drink it once the afternoon is over, you can say bye-bye to an early night.
According to new research published in the journal Science Translation Medicine, the drink is more than just a stimulant – it actually slows down the body's internal clock, making it much more difficult to switch off at night.
In fact, the US researchers who carried out the study found that drinking a double espresso three hours before snuggling under the duvet stalls the production of melatonin – the hormone that induces sleep at night time – by around 40 minutes.
The equivalent effect would be standing under bright light for three hours directly before going to bed. In the paper, they note:
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.
They made the discovery by conducting two experiments. In the first, they kept five volunteers under tightly controlled conditions for 49 days, giving them either a double espresso caffeine dose or a placebo shortly before bedtime.
In the second, they treated cultured cells with caffeine to see what impact it had on individual cells' circadian rhythm. In both cases, they found a noticeable slowdown in the release of the sleep hormone.
But while this is a big warning to all insomniacs who have a habit of drinking coffee in the evenings, the report notes that these findings could potentially have some uses:
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.