{
  "schema_version": 1,
  "id": "caffeine-dose-timing-sleep-boundary-2025",
  "canonical_url": "https://brali-lifeos.github.io/evidence/caffeine-dose-timing-sleep-boundary-2025/",
  "json_url": "https://brali-lifeos.github.io/evidence/caffeine-dose-timing-sleep-boundary-2025/index.json",
  "decision": "support-existing",
  "decision_label": "Supports existing guidance",
  "reviewed_at": "2026-09-06",
  "reviewed_by": "Brali Evidence Reviewer",
  "source": {
    "title": "Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial",
    "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC11985402/",
    "type": "primary-study",
    "doi": "10.1093/sleep/zsae230",
    "citation_text": "Gardiner CL, Weakley J, Burke LM, et al. Sleep. 2025;48(4):zsae230.",
    "study_design": "Placebo-controlled, double-blind randomized crossover trial with seven conditions separated by 48-hour washouts. Participants received placebo or a single 100 mg or 400 mg caffeine dose 12, 8, or 4 hours before habitual bedtime; sleep was assessed with in-home partial polysomnography and sleep diaries.",
    "population": "23 healthy males aged 18–40 years (mean age 25.3 years) with moderate habitual caffeine intake below 300 mg per day.",
    "intervention_or_exposure": "Acute caffeine anhydrous capsules containing 100 mg or 400 mg, administered once at 12, 8, or 4 hours before habitual bedtime, compared with placebo.",
    "outcomes": [
      "Objective total sleep time",
      "Sleep efficiency",
      "Sleep onset latency and latency to persistent sleep",
      "Wake after sleep onset and awakenings",
      "Sleep-stage distribution including N3 sleep",
      "Subjective total sleep time and sleep quality"
    ]
  },
  "supported_claim": "Caffeine timing should be interpreted together with dose rather than as one universal after-lunch rule. In this small randomized crossover trial, a single 400 mg dose disrupted multiple objective sleep measures when taken within 12 hours of bedtime, with larger disruption closer to bedtime; no statistically significant sleep effect was detected for 100 mg at the tested 12-, 8-, and 4-hour timings. For Brali, this supports moving large late-day caffeine doses earlier when sleep matters and using bedtime-relative timing rather than a fixed clock cutoff.",
  "unsupported_or_overstated_claims": [
    "Everyone should stop caffeine at 1 p.m. or immediately after lunch.",
    "A 100 mg dose four hours before bedtime is safe or sleep-neutral for every person.",
    "Twelve hours is a scientifically established cutoff for every caffeine dose or pattern of use.",
    "People can infer whether they metabolize caffeine quickly from whether they fall asleep after an afternoon coffee.",
    "The study establishes an ideal daily caffeine dose, a body-weight dosing range, or a morning dosing schedule.",
    "The trial tested ordinary coffee, tea, energy drinks, or repeated real-world servings rather than standardized caffeine capsules.",
    "A personal sleep log can establish a causal individual caffeine dose-response curve."
  ],
  "limitations": [
    "The sample was small (23 participants) and included only healthy men aged 18–40, limiting generalizability to women, older adults, adolescents, people with sleep disorders, and other populations.",
    "Participants were moderate habitual caffeine users; results may differ in people with very low, very high, or irregular caffeine exposure.",
    "The intervention used acute standardized caffeine capsules rather than the variable doses, ingredients, absorption patterns, and repeated servings found in real-world caffeinated products.",
    "The study tested only two caffeine doses and three pre-bed timing points, so it cannot define a continuous or personalized cutoff.",
    "Sleep was measured with in-home partial polysomnography rather than full laboratory polysomnography.",
    "A nonsignificant result for 100 mg in this sample is not proof of no effect for every individual, especially given known variability in caffeine pharmacokinetics and sensitivity."
  ],
  "target_hack_ids": [
    "stop-caffeine-after-lunch"
  ],
  "target_protocol_ids": [
    "brali:stop-caffeine-after-lunch"
  ],
  "risk_flags": [
    "health"
  ],
  "notes": "Editorial action: replace the inherited fixed after-lunch/1 p.m. rule with a dose-aware, bedtime-relative protocol. Start with the highest-leverage low-risk change: move large late-day doses earlier or reduce them. Let users track last caffeine timing/rough amount and broad sleep/daytime-function trends without deliberately challenging themselves with late caffeine. Keep the 100 mg null finding as an evidence boundary, not a clearance rule."
}