Research brief · Randomized crossover trial
Caffeine and sleep: dose and timing in a small trial
A crossover trial tested 100 mg and 400 mg of caffeine at different times before bedtime. The findings help frame questions about both dose and timing.
Who took part, and how?
Twenty-three healthy men, averaging about 25 years old, completed placebo and caffeine conditions in a double-blind crossover trial. Researchers tested 100 mg and 400 mg doses taken 4, 8, or 12 hours before bedtime and measured sleep at home.
What did the study find?
The 400 mg dose disrupted aspects of sleep even when taken 12 hours before bedtime. The study found no statistically significant sleep effects from the 100 mg dose at the tested times.
What are the limits?
This was a small, short-term study in men with moderate habitual caffeine intake. It does not establish a universally safe dose or cutoff time, and a nonsignificant finding does not prove that caffeine has no effect.
What can a reader take away?
Consider both how much caffeine you consume and when. Your own response may differ.
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