Sleep
Caffeineand REM sleep
Only one source here so far, and it found no clear difference in REM sleep.
How sure anyone can be
Very low certainty, level 1 of 4Any estimate here is very uncertain.
The numbers reported
No number has been put on this yet. One source recorded only which way the numbers went — for now, that is all we have here.
One source, newest first
What we read is the published abstract, not the full paper, so a blank below may still be printed in the paper itself. A fixed rule worked this out from the source’s own fields. Nobody checked this rating by hand.
Systematic review, 2025
Very low certainty, level 1 of 4Age- and dose-specific effects of caffeine on sleep: A meta-analysis of controlled crossover trials.
Sleep Med. 2025;136:106874. doi:10.1016/j.sleep.2025.106874. PMID:41124973.
- Number reported
- Not in the abstract
- Which way it went
- No clear difference
- Likely range
- Not in the abstract
- Source’s own words
- percentage of sleep spent in REM, mean difference vs placebo (magnitude not reported)
- Who was studied
- Adult
- Compared with
- placebo
- Amount taken
- Not in the abstract
- For how long
- Not in the abstract
- Disagreement between studies
- Not in the abstract
- Kind of record
- Journal article
How this rating was reachedstarts at High, 3 steps down: risk of bias, indirectness and imprecision
- Starts at High
- Risk of bias brought it down to Moderatethe abstract reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
- Indirectness brought it down to Lowthe outcome measured is a proxy for the target outcomeReported in the abstract
- Imprecision brought it down to Very lowthe abstract reports no confidence interval for the estimateNot in the abstract
- Ends at Very low3 steps down.
- Inconsistency
- No disagreement reported, and no count of studies behind it
Imprecision stops at the first check that applies; others may apply too.
AI-reviewed & signed — an AI agent re-read this finding against the saved source and checked that the quote, the numbers, the units and the direction match it. No person read it. The owner authorised the agent to sign the batch with the owner's key, and every build rechecks that signature against these exact bytes.
What is still missing from these readings
- No number at all, only which way it went.
- One gives no likely range, so how precise that number is is unknown.
- One do not say how many people took part.
- Amount taken — Not in the abstract.
- For how long — Not in the abstract.
Something nobody wrote down is never a zero and never a guess.
Still to read for Caffeine
Ten of the 19 things on our list for Caffeine have no reading here yet:
- Anxiety
- Cognitive performance
- Estimated VO2max
- Fatigue
- Heart rate variability (RMSSD)
- Light sleep
- Number of awakenings
- Resting heart rate
- Serum cortisol (morning)
- Wake after sleep onset (WASO)
Still to read means nobody here has got to it, not that it was tried and did nothing or that no research exists. A pairing on no list is not a gap: we never set out to read it.
Read next
Caffeine
Eight other questions read for it
Sleep
28 questions read under it
REM sleep
No other ingredients read against it
Alphabetical, and by nothing else.
This is a library, not advice. No recommendation, no dose, no diagnosis, no ranking. We never ask about your symptoms, and nothing here is tailored to you.