Caffeine intake and subsequent sleep quality
While general advice suggests avoiding caffeine close to bedtime, there is some debate about how long one should avoid caffeine for prior to retiring for the night. Could caffeine in the late afternoon, for example, influence sleep?
In a recent study by researchers from the Henry Ford Hospital, Detroit, 12 healthy participants were instructed to ingest three pills a day, for four days, at specific intervals (0,3,6 hrs before bedtime). One pill contained a fixed dose of caffeine (400mg, equivalent to 2-3 cups of standard coffee), while the other two pills were placebos. On one day out of the four, all three pills were placebos. This way, the researchers were able to directly compare timing of caffeine intake and subsequent effects on sleep.
Sleep was assessed through self-report and objectively, using a portable brain monitoring device. The main findings were that, relative to placebo, caffeine at 0 and 3 hours prior to sleep negatively affected both objective (sleep latency, total sleep time) and subjective measures of sleep. Interestingly, ingesting caffeine 6 hours prior to sleep had similar effects to the other caffeine times, reducing total sleep time by approximately 1 hour, relative to placebo. Conversely, however, subjects did not reliably report that sleep was subjectively affected in the 6 hour condition. Moreover, ingesting 6 hours prior to sleep increased wake time during the night, reduced sleep efficiency and time spent in slow wave sleep (relative to placebo).
Findings provide support for the widely promoted sleep hygiene advice, that caffeine should be avoided for a minimum of 6 hours prior to bedtime.
Drake, C., Roehrs, T., Shambroom, B.S., Roth, T. (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11), 1195-1200.