RCTHumann = 232025
Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial.
Plain-language summary
This study tested how different doses and timing of caffeine affect sleep in men who usually drink moderate amounts. It compared a placebo, 100 mg, and 400 mg of caffeine taken at 12, 8, or 4 hours before bedtime, using sleep tracking and diaries. The 100 mg dose did not disrupt sleep, but 400 mg delayed sleep onset when taken within 12 hours of bedtime and worsened sleep quality when taken within 4 hours. The study also found that people may not always notice how caffeine affects their sleep.
Key findings
- 100 mg of caffeine did not affect sleep, even when taken 4 hours before bedtime.
- 400 mg of caffeine delayed sleep onset when taken within 12 hours of bedtime.
- 400 mg of caffeine worsened sleep quality when taken within 4 hours of bedtime.
- People may not accurately perceive how caffeine affects their sleep.
How to analyze the study yourself
- Study type
- Randomized trials assign people to groups by chance, so differences between groups are unlikely to come from who chose what, but the small sample size and specific population may limit generalisability.
- Population
- Young men with moderate caffeine habits, under 300 mg a day.
- Funding
- Not reported
- Takeaway
- This study found that a 100 mg dose of caffeine (about one cup of coffee) did not disrupt sleep, even when taken 4 hours before bed, but a 400 mg dose (about four cups) delayed sleep onset when taken within 12 hours of bedtime and worsened sleep quality when taken within 4 hours. If you're sensitive to caffeine or struggle with sleep, it may be worth keeping your intake under 100 mg in the evening.