For instance, when compared to placebo, taking caffeine at 400mg four hours prior to sleep would reduce total sleep time by an estimated 50.6 minutes.
In contrast, taking a lower dose of caffeine, specifically at 100mg, even at four hours prior to bed, would not significantly affect total sleep duration or the time taken to fall asleep.
A group of researchers from Australian Catholic University and Monash University reported the findings in the journal Sleep.
The findings are according to a 21-day placebo-controlled, double-blind, randomised crossover study involving 23 young men with the median age of 25.3 ± 5.0 years old.
To find out the impact of different caffeine on sleep patterns, the participants were randomised into seven groups where they took a capsule containing either 1) placebo or 2) caffeine at 100mg or 3) 400mg three times a day.
The three timings were at 12 hours, eight hours, and four hours before bed.
One group took placebo capsules at all three timings.
The other six groups took placebo capsules at two timings. Their third capsule would be one containing either 100mg or 400mg of caffeine, taken at either 12 hours, eight hours, or four hours before bed.
The dose of 100mg was chosen because that is equivalent to that of a cup of coffee, while the 400mg dose is the upper recommended daily limit.
Impact of caffeine on sleep was assessed by collecting saliva samples, measuring sleep duration using a device, as well as a questionnaire.
The device, in this case, Somfit, calculated the participants’ total sleep time, sleep efficiency, latency to persistent sleep, rapid eye movement sleep onset latency, wake after sleep onset, number of awakenings per hour.
The questionnaire, on the other hand, looks at the participants’ perceptions of their total sleep hours and sleep quality.
Findings showed that at an hour after caffeine consumption, salivary caffeine concentration was significantly higher in the groups that took caffeine, be it 100mg or 400mg, as compared to the group which took purely placebo capsules.
The 400mg group also had significantly higher caffeine concentration as compared to the 100mg group.
In terms of objective sleep outcomes, no significant disruption to sleep was observed in the 100mg group.
However, the 400mg group reported significantly greater disruptions to their sleep when caffeine was taken four hours before sleep.
As compared to the placebo, their total sleep time was reduced by an estimated 50.6 minutes and reduced by 46.2 minutes when compared to the 100mg group.
Sleep duration was also reduced when 400mg of caffeine was taken eight and 12 hours before sleep, but the reduction was not statistically significant.
Longer time to fall asleep
The group taking 400mg of caffeine at four hours before sleep also reported taking a significantly longer time to fall asleep.
Their sleep onset latency or the time it takes to fall asleep was about 14.2 minutes longer as compared to the placebo.
They also experienced significant reduction in sleep efficiency – commonly defined as ratio of total sleep time to time in bed – as compared to the placebo.
Their sleep efficiency was 9.5 per cent lower as compared to the placebo.
Significant reduction in sleep efficiency was also reported in the group taking 400mg of caffeine eight hours before bed. In this case, their sleep efficiency was lower by 6.9 per cent as compared to the placebo.
There was also an estimated increase of 1.4 awakenings per hour in the group taking 400mg of caffeine four hours prior to bed.
Subjective sleep outcomes
The group taking 400mg of caffeine four hours before sleep also reported significant differences in their subjective sleep outcomes.
For instance, their pre-sleep alertness was significantly increased by about 0.65 units and perceived sleep onset latency was increased by 31.3 minutes.
They also reported feeling less sleepy and a lower sleep quality.
“Importantly, 400 mg of caffeine negatively impacted perceptions of sleep quantity and quality when consumed four hours prior to bedtime, but not when consumed eight or more hours away from bedtime.
“A high dose of caffeine (400 mg) consumed as one dose in the morning is detrimental to subsequent night-time sleep, with greater disruptions the closer consumption occurs to bedtime,” the researchers concluded.
Source: Sleep
Dose and timing effects of caffeine on subsequent sleep: A randomised clinical crossover trial
https://doi.org/10.1093/sleep/zsae230
Authors: Carissa L Gardiner et al
