The impact of daily caffeine intake on nighttime sleep in young adult men.
Plain-language summary
This study set out to see whether a regular daytime coffee habit disturbs sleep in young men who already drink it. Twenty men went through three 10 day conditions, daily caffeine at 150 mg three times a day, caffeine withdrawal, and a dummy pill, with the last dose 8 hours before a scheduled night's sleep. Total sleep time, how long they took to fall asleep, sleep structure and how good sleep felt did not show a significant change between the three. Brain wave activity in one narrow band during non-REM sleep was lower under both caffeine and withdrawal, which the authors read as a possible early withdrawal effect. Another study here, on blood caffeine levels and sleep depth, comes from the same research group and uses the same kind of design.
Key findings
- Daily caffeine intake did not affect total sleep time, sleep latency, or subjective sleep quality.
- EEG power density in the sigma range (12-16 Hz) during non-REM sleep was reduced in caffeine and withdrawal conditions.
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.
- Population
- Twenty male young habitual caffeine consumers
- Funding
- Not reported
- Takeaway
- This study found that caffeine taken in the morning and afternoon, with the last dose 8 hours before bed, did not show a significant change in sleep for men who drink it habitually. If you keep your coffee to the daytime and leave a long gap before bed, this suggests the habit itself is not what is costing you sleep. It says nothing about drinking it in the evening.