Bedtime coffee myth put to rest

Caffeine is a known powerful stimulant that 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 affect sleep at all.

Researchers from Florida Atlantic University and Harvard Medical School recorded how much caffeine, alcohol and nicotine 785 volunteers consumed, and compared their sleep diaries and data from wrist sensors.

About 40 per cent of the group admitted consuming caffeine on at least one night of the study. But although nicotine and alcohol did disrupt sleep – with a night-time cigarette knocking 42 minutes off total sleep for insomniacs – caffeine appeared to have no effect.

The findings were unexpected, as physiologically, caffeine blocks sleep-promoting chemicals in the brain.

Writing in the journal Sleep, Dr Christine Spadola, of the Florida university, said: ‘‘These findings support the importance of sleep health recommendations which promote the restriction of evening nicotine and alcohol.’’

A report by the Sleep Council has found that 70 per cent of adults in Britain get fewer than seven hours’ sleep a night, and more than a quarter regularly sleep poorly.

Doctors have recommended cutting down on tea, coffee, energy drinks or cola in the evening, because caffeine is thought to interfere with the process of falling asleep and prevents deep sleep, recommending instead warm milky drinks or herbal teas. The advice is based on previous research that showed caffeine use close to bedtime appeared to increase the time it took to fall asleep and made people wake sooner.

But the researchers said most previous studies involved fewer participants in unnatural laboratory settings, where they were given caffeine tablets to mimic the effects of night-time drinks.