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Open WellbeingWhat the studies actually measured

Heart and blood pressure

Caffeineand Diastolic blood pressure

Both sources here measured higher diastolic blood pressure.

How sure anyone can be

Low certainty, level 2 of 4

Further research is likely to change this.

The most certain of the two findings here; each record carries its own.

The numbers reported

One source’s range, drawn against its own line of no difference and scaled to its own numbers.

0.751.66 mmHg2.57

This range stays on one side of the no-difference line.

Bar the confidence interval — the range the true effect is likely to sit inNotch the number the source reportedLine where there would be no difference at all

Two sources, 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, 2023 · 8 studies pooled

    Low certainty, level 2 of 4

    The effects of caffeine supplementation on blood pressure in adults: A systematic review and dose-response meta-analysis.

    Clin Nutr ESPEN. 2023;58:165-177. doi:10.1016/j.clnesp.2023.09.923. PMID:38057002.

    Number reported
    1.66 mmHg
    Which way it went
    Higher
    Likely range
    0.75 to 2.57
    Source’s own words
    mmHg diastolic, weighted mean difference vs control
    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, 2 steps down: risk of bias and imprecision
    1. Starts at High
    2. 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
    3. Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
    4. Ends at Low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    No high disagreement reported between the 8 studies it pooled

    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.

    Read the abstract on PubMed

  • Systematic review, 2005 · 7 studies pooled

    Low certainty, level 2 of 4

    Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials.

    J Hypertens. 2005;23(5):921-8. doi:10.1097/01.hjh.0000166828.94699.1d. PMID:15834273.

    Number reported
    2.41 mmHg
    Which way it went
    Higher
    Likely range
    0.98 to 3.84
    Source’s own words
    mmHg diastolic, mean difference vs control, caffeine-tablet trials only
    Who was studied
    Adult
    Compared with
    control arm of randomised trials lasting at least 7 days
    Amount taken
    410 mg/d median dose in the caffeine-tablet stratum
    For how long
    7 days (upper bound: Not in the abstract)
    Disagreement between studies
    Not in the abstract
    Kind of record
    Journal article
    How this rating was reachedstarts at High, 2 steps down: risk of bias and imprecision
    1. Starts at High
    2. 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
    3. Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
    4. Ends at Low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    No high disagreement reported between the 7 studies it pooled

    Imprecision stops at the first check that applies; others may apply too.

    AI review could not confirm it — an AI agent re-read this finding against the saved source and at least one check failed. The batch record names the check and quotes the sentence that caused the doubt. No person read it.

    Read the abstract on PubMed

What is still missing from these readings

  • Two do not say how many people took part.
  • Amount taken — One of Two readings: Not in the abstract.
  • For how long — One of Two readings: 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

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.