If you’ve ever hesitated about saying yes to that offer of a coffee after dinner or cup of tea before bed, you can now stop worrying, say scientists.
Drinking caffeine close to bedtime may not stop you getting you off to sleep after all, a study suggests. Instead, it is alcohol which is far more likely to lead to a night of tossing and turning.
Researchers tracked the sleep of nearly 800 people over six nights, and asked them to note if they had consumed caffeine, alcohol or nicotine in the four hours before bed.
Almost half had caffeinated drinks at night but no link with poor sleep could be found. In contrast, those who drank alcohol saw their sleep efficiency fall by almost 1% – the equivalent of five minutes’ lost sleep. Those who smoked before bed saw a 2% fall in their sleep efficiency, an average of eight extra minutes awake.
The study, published in the journal Sleep, did not take into account how much caffeine the participants drank or how sensitive they were to it. Some people break it down in their bodies faster than others.
Lead author Dr Christine Spadola, of Florida Atlantic University, said: "While we did find that evening consumption of alcohol and nicotine were associated with sleep disruption, we did not find an association between consumption of caffeine within four hours of bedtime and sleep disruption.
"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.
"However, it is important to note that we did not look at caffeine dosing or individual tolerance and sensitivity levels, which are important factors that can impact the effect caffeine on one’s sleep. Overall, it is best to limit caffeinated drinks after 12 noon for optimal sleep."
Alcohol affects chemicals in the brain and is known to cause shallower sleep. Caffeine and nicotine are stimulants which can block chemicals important for sleep.