Drinking coffee or tea within four hours of bedtime does not affect sleep, a study has found.
Researchers from Florida Atlantic University and Harvard Medical School recorded caffeine, alcohol and nicotine consumption among 785 volunteers and compared daily sleep diaries and data from wrist sensors.
Around 40% of the group consumed caffeine on at least one night of the study, which was carried out for an average of 6.7 nights.
The study found that while nicotine and alcohol disrupted sleep – with a late cigarette taking 42 minutes off total sleep for insomniacs – caffeine seemed to have no effect.
Writing in the journal Sleep, Dr Christine Spadola, of Florida Atlantic University, said: “Considering the public health importance of obtaining quality sleep and the widespread use of alcohol, nicotine and caffeine, relatively few studies have thoroughly investigated the association between evening substance use and sleep parameters.
“This study represents one of the largest longitudinal examinations of the associations of evening use of alcohol, caffeine and nicotine with objectively measured sleep outcomes.
“A night with use of nicotine and/or alcohol within four hours of bedtime demonstrated worse sleep continuity than a night without.
“We did not observe an association between ingestion of caffeine within four hours of bed with any of the sleep parameters.”
“This was a surprise to us but is not unprecedented. The previous evidence is mixed when it comes to the effect of caffeine on sleep,” Dr Spadola said.
She added that the findings “support the importance of sleep health recommendations which promote the restriction of evening nicotine and alcohol”.
Nicotine was the substance most strongly associated with sleep disruption. There was a statistically significant interaction between evening nicotine use and insomnia in relation to sleep duration.
Among participants with insomnia, nightly nicotine use was associated with an average 42.47-minute reduction in sleep duration.
The NHS recommends cutting down on tea, coffee, energy drinks or cola before bed as caffeine is thought to interfere with the process of falling asleep.