RESEARCH · 2013
Why the coffee nap belongs in the early afternoon
Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. 2013;9(11):1195–1200.
At a glance
- Who
- 12 healthy adults aged 19–48, sleeping at home
- Setup
- Randomized, double-blind and placebo-controlled: everyone tried every condition without knowing which pill was which
- Compared
- 400 mg of caffeine at bedtime, 3 hours before or 6 hours before, and a placebo
- Finding
- Caffeine disturbed sleep at all three times. Even 6 hours before bed it cut total sleep by more than an hour.
What they did
Sleep advice often says to stop caffeine in the afternoon, but there was little hard data on how early is early enough. Researchers at the Henry Ford Hospital sleep center gave volunteers 400 mg of caffeine, about four cups of brewed coffee, at three different times before their usual bedtime, and a placebo on other days. Sleep was measured with a portable sleep monitor and a sleep diary.
What they found
- Caffeine disturbed sleep whether it was taken at bedtime, 3 hours before or 6 hours before.
- Even at 6 hours before bed, the monitor measured more than an hour less sleep.
- People's own sleep diaries didn't show that loss as clearly: they often didn't realize their sleep had suffered.
What it means for your coffee nap
Plan the coffee nap for the early afternoon, and at least 6 hours before you go to bed. A coffee nap usually uses less caffeine than this study (100–200 mg rather than 400 mg), which probably means a smaller effect, but the study didn't test smaller doses. If you need a boost in the evening, take a power nap without coffee instead.
Limits
Twelve people and one fairly large dose. Caffeine sensitivity varies a lot from person to person: its half-life is about 5 hours on average, but much longer for some people.