Caffeine is known to be a powerful stimulant which perks up drinkers, increases alertness and promotes wakefulness.
Yet a surprising new study has found that drinking tea or coffee within four hours of bedtime does not actually impact sleep at all.
US researchers from Florida Atlantic University and Harvard Medical School monitored 785 people for a total of 5,164 days and nights, recording how much caffeine, alcohol and nicotine they consumed.
They then compared it to sleep diaries and wrist sensors which recorded sleep duration, sleep efficiency and how quickly people woke up after drifting off.
Around 40 per cent of the group admitted to drinking caffeine on at least one night of the study….