1. Substance and claimed effects

Creatine is a nitrogen-containing organic acid synthesised endogenously from arginine, glycine, and methionine (about 1 g/day in a 70 kg adult) and obtained dietarily from red meat and fish (roughly 1–2 g/day in an omnivorous diet). Approximately 95% of total body creatine is stored in skeletal muscle, two-thirds as phosphocreatine, where it serves as a rapid phosphate donor for ATP regeneration during high-energy demand Kreider et al. 2017. Creatine monohydrate is the form used in essentially all positive trials; alternatives (HCl, ethyl ester, buffered "Kre-Alkalyn") have no demonstrated superiority and ethyl ester degrades to inert creatinine in transit Antonio et al. 2021.

This entry covers creatine monohydrate supplementation at 3–5 g/day in healthy adults, and every meaningful consequence the literature attaches to it: muscle mass and strength when paired with resistance training, cognitive performance (especially under stress, sleep deprivation, or in vegetarians), depressive-symptom severity as adjunct or standalone, bone mineral density preservation in postmenopausal women on a training programme, and downstream effects on energy floor, healthy aging, and appearance. The dossier weighs each consequence on its own evidence base — they are not uniformly strong.

2. Evidence by addressing question

Mechanism

Creatine's bioenergetic role is settled. Phosphocreatine donates its phosphate group to ADP via creatine kinase to regenerate ATP in approximately 1–10 second timescales — the rate-limiting fuel for short, intense efforts and the immediate buffer when ATP demand spikes Kreider et al. 2017. Muscle stores saturate at roughly 150–160 mmol/kg dry muscle; supplementation raises a typical omnivore's resting concentration (120 mmol/kg) by 15–20%, with larger relative gains in vegetarians whose baselines run 20–30% lower Burke et al. 2003.

The brain story is parallel and increasingly well-mapped. Creatine crosses the blood-brain barrier, albeit slowly (weeks to months for full equilibration), and supports the same ATP-regeneration role in tissues with high energetic demand. Gordji-Nejad et al. 2024 demonstrated that a single high dose (0.35 g/kg, ~25 g for a 70 kg adult) raised cerebral phosphocreatine and ATP measurable on ³¹P-MRS within 4 hours and prevented the bioenergetic decline normally seen during 21-hour sleep deprivation. The mechanistic chain — phosphocreatine availability → neuronal ATP buffering → preserved cognitive performance under high metabolic stress — is internally consistent.

The mood mechanism is less direct but biologically plausible: phosphocreatine is depleted in the frontal cortex of depressed patients on ³¹P-MRS, antidepressant response correlates with restoration, and oral creatine raises brain creatine/phosphocreatine in the same regions Lyoo et al. 2012.

For bone, the candidate mechanism is two-pronged: (i) increased mechanical loading via greater muscle mass and training capacity, and (ii) a direct effect on osteoblast bioenergetics during bone-formation cycles Chilibeck et al. 2015. The direct-bone mechanism is plausible but less established than the muscle-derived loading explanation.

Evidence — muscle and strength

Among supplements, creatine has the largest and most consistently replicated effect on resistance-training outcomes. The Lanhers et al. 2017 meta-analysis of upper-limb strength performance pooled 53 trials and found significant improvements across exercise durations under 3 minutes (SMD 0.265, p < 0.001), with consistent direction across bench-press, biceps curl, and chest-press protocols. Chilibeck et al. 2017 pooled 22 trials in adults aged 57–70 and reported an additional lean-tissue gain of 1.37 kg (95% CI 0.97–1.76) over resistance training alone, plus measurable chest-press and leg-press strength advantages, after 7–52 weeks of supplementation. Effect direction is robust to age, sex, and training status; magnitude scales with training stimulus.

The training-dependence is load-bearing for the rating: creatine without resistance work produces small body-water and muscle-volumization effects but not the durable strength/hypertrophy gains the literature attributes to it. The ~1–2 kg early weight gain (largely intramuscular water) is real but is not the lasting effect Antonio et al. 2021.

Evidence — cognition

The cognition literature is more heterogeneous. Rae et al. 2003 (n=45 vegetarians, 5 g/day × 6 weeks, double-blind crossover) reported large effects on backward digit span (working memory) and Raven's Advanced Progressive Matrices (fluid intelligence) — both speed-of-processing tasks. Avgerinos et al. 2018, in a systematic review of 6 RCTs, concluded short-term memory and reasoning may be improved by creatine, with effects most consistent in vegetarians and under conditions of mental stress; results were null in young omnivores on routine cognitive batteries.

Two recent contributions tighten the picture. Prokopidis et al. 2023 meta-analysed memory outcomes and found a substantial effect in older adults aged 66–76 (SMD 0.88, 95% CI 0.22–1.55) but no effect in younger adults aged 11–31 (SMD 0.03). Sandkühler et al. 2023 ran a preregistered crossover trial in 123 healthy adults (mixed vegetarian/omnivore, 5 g/day × 6 weeks) and found borderline benefit on backward digit span (p = 0.064) but no clear advantage on Raven's matrices, with Bayesian evidence supporting a small effect overall. Crucially, vegetarians did not benefit more than omnivores in this trial — challenging the long-standing assumption that baseline depletion is the modifier.

The strongest single-trial cognition result remains Gordji-Nejad et al. 2024: a single 0.35 g/kg dose preserved working memory, processing speed, and psychomotor vigilance against the deficits induced by 21-hour sleep deprivation, with parallel neuroimaging confirmation of brain bioenergetic effects. This is a high-stress, acute-dose finding — not the standard 3–5 g/day chronic protocol — but it directly supports the mechanism.

Evidence — mood and depression

The depression literature is small but consistent in direction. Roitman et al. 2007 open-label add-on (8 patients with treatment-resistant depression, 3–5 g/day × 4 weeks on top of existing antidepressants) reported 7/8 unipolar patients improved significantly; notably, both bipolar patients developed hypomania/mania, flagging a real safety signal. Lyoo et al. 2012 — the largest controlled trial to date (n=52 women with MDD on escitalopram, 3 g/day week 1 then 5 g/day weeks 2–8, double-blind placebo-controlled) showed significantly greater HAM-D improvement in the creatine arm as early as week 2, sustained to week 8. Bakian et al. 2020 NHANES analysis (n=22,692) found dietary creatine intake inversely associated with depression prevalence (lowest vs. highest quartile AOR 0.68; AOR 0.62 in women, 0.58 in non-antidepressant users) — observational, but biologically aligned with the trial signal.

The recent Antonio et al. 2021 ISSN review summarises this as "moderate-to-large effect sizes in small trials, with the largest signal in women and in clinically depressed populations." A 2025 BJN meta-analysis (Eckert et al.) pooled 11 trials (n=1,093), found SMD −0.34 favouring creatine but flagged very-low-certainty evidence and trim-and-fill bias adjustments favouring creatine — meaning the published effect may overstate. The honest read: the signal is real and the mechanism is plausible, but the trials are still small and biased, and most lacked placebo arms.

Evidence — bone density

The strongest trial is Chilibeck et al. 2015: 12 months, n=33 postmenopausal women, randomised double-blind to creatine 0.1 g/kg/day plus resistance training (3×/week) vs. placebo plus training. Femoral neck BMD declined 1.2% in the creatine arm versus 3.9% in placebo (p < 0.05) — a 70% reduction in the rate of hip-bone loss over a year. Femoral shaft subperiosteal width — a predictor of bone bending strength — increased in the creatine arm. The effect requires the resistance-training pairing; creatine alone in non-training postmenopausal women has not shown bone preservation in controlled trials. Replication is limited — the 2-yr follow-up trial showed similar direction but smaller effect, and several null trials exist in older mixed-sex populations — so the rating is "real and replicated in the most-affected subgroup, not yet dominant."

Protocol

Two equivalent routes to muscle saturation. Hultman et al. 1996 demonstrated that 20 g/day for 6 days followed by 2 g/day maintenance produced the same final muscle creatine concentration as 3 g/day from day one — the loading route reaches saturation in about a week, the no-loading route takes roughly 28 days. Kreider et al. 2017 ISSN consensus is 3–5 g/day creatine monohydrate as the default protocol, scaling to 0.03 g/kg for body size if precision matters; loading (0.3 g/kg/day for 5–7 days) is optional and recommended only when faster effect is needed. Timing within the day appears immaterial; co-ingestion with carbohydrate or protein modestly enhances uptake but does not change saturation ceiling.

Form: creatine monohydrate. Cost: roughly $15–30 per year per person at typical doses. Cycling is not necessary and has no documented benefit Antonio et al. 2021.

Contraindications

The literature supports a strong safety profile in healthy users across all ages, with the Kreider et al. 2017 ISSN position stand pooling over 1,000 trials and finding no credible evidence of renal, hepatic, or cardiovascular harm at doses up to 30 g/day for 5 years.

Clinically meaningful contraindications:

• Pre-existing kidney disease. The healthy-kidney evidence does not generalise to compromised renal function; conservative practice is to avoid supplementation in CKD without nephrology oversight Antonio et al. 2021.
• Bipolar disorder. Roitman et al. 2007 documented mania/hypomania induction in 2/2 bipolar patients; the signal is small but the mechanism (energetic upregulation in the same brain regions implicated in mania) is plausible. Bipolar augmentation should be clinician-supervised at minimum.
• Spurious creatinine elevation. Supplementation raises serum creatinine by 10–20% via increased substrate availability, not via renal damage. A clinician unaware of supplementation may misread this as kidney decline Antonio et al. 2021. Action: disclose use before blood work or request cystatin-C as an alternative GFR marker.

Pregnancy/breastfeeding data are limited; absence of harm signal but not enough trials to recommend routinely.

Misconceptions

The persistent reader-facing misconceptions, ordered by frequency:

• "Creatine damages kidneys." Originated from a 1998 case report and the serum-creatinine artefact above. Multiple long-term trials (up to 5 years) and the ISSN position stand find no renal harm in healthy users Kreider et al. 2017.
• "You have to load." Loading accelerates saturation by about three weeks; the endpoint is identical at 28 days on 3 g/day Hultman et al. 1996.
• "It causes hair loss / DHT spike." Based on a single 2009 rugby-player trial reporting a non-significant DHT change, never replicated, and no trials showing actual hair loss Antonio et al. 2021.
• "It's only for bodybuilders." The cognition, mood, sleep-deprivation, and bone-density evidence is non-athletic; older adults and women are arguably the highest-yield population Smith-Ryan et al. 2021.
• "It causes bloating." The 1–2 kg early weight gain is largely intramuscular water, which improves muscle appearance ("fullness"), not subcutaneous water that causes the puffy look Antonio et al. 2021.
• "Need fancy forms — HCl, ethyl ester." Monohydrate has near-100% bioavailability; ethyl ester degrades to inert creatinine in transit; HCl is more soluble but produces equivalent muscle creatine at matched doses, at 3–10× the cost Antonio et al. 2021.

Audience and population variability

Larger effects, ranked by signal strength:

• Vegetarians and vegans. Baseline muscle creatine is 20–30% lower; absolute gain from supplementation is correspondingly larger. Burke et al. 2003 demonstrated greater muscle creatine and fibre-area changes in vegetarian trainees vs. omnivores; Rae et al. 2003 selected vegetarians specifically for the cognition trial on this basis. Sandkühler et al. 2023 failed to replicate the vegetarian-specific cognitive advantage, leaving the muscle/strength benefit better-evidenced than the cognitive one for this subgroup.
• Older adults. Chilibeck et al. 2017 meta-analysis showed +1.37 kg lean mass advantage in adults 57–70 on training programmes; Prokopidis et al. 2023 showed memory benefits concentrated in the 66–76 age band. The age-creatine interaction is consistent across muscle and cognition.
• Postmenopausal women. Chilibeck et al. 2015 femoral neck BMD preservation; Lyoo et al. 2012 mood effect was women-specific by design. Smith-Ryan et al. 2021 reviews evidence that endogenous creatine pools are 70–80% smaller in women than men, with hormonal modulation across menstrual cycle, pregnancy, and menopause.
• Sleep-deprived adults. Gordji-Nejad et al. 2024; relevant for night-shift workers, new parents, on-call clinicians.
• TBI / neurodegeneration. Sakellaris et al. 2006 pediatric pilot showed cognitive and behavioural improvements at 0.4 g/kg/day in TBI recovery; this is suggestive, not catalogue-relevant for general adult guidance.

Non-responders: roughly 20–30% of users have minimal muscle creatine response to standard dosing — typically because baseline stores are already near saturation (high-meat diet) or because of polymorphisms in the creatine transporter. Not predictable in advance; the safe default is to try 3–5 g/day for 8 weeks and assess.

Alternatives

For muscle/strength: protein adequacy (1.6 g/kg/day) and progressive resistance loading are the higher-leverage interventions; creatine is additive on top, not a substitute. For cognition: sleep, stimulants (caffeine), and aerobic exercise have larger and better-replicated effects. For mood: SSRIs, exercise, and CBT have substantially stronger evidence; creatine is plausible adjunct. For bone: weight-bearing exercise, vitamin D adequacy, and bisphosphonates (where indicated) lead; creatine plus training is supplementary.

Failure modes

Common reasons users report "creatine didn't work":

• Inconsistent dosing. Effect is gated on muscle saturation; missing 4+ days/week prevents reaching it. Daily is daily — not "training days only."
• No resistance training. The muscle/strength effects are training-stimulus-multiplied. Sitting on the couch with creatine produces water-weight gain and not much else.
• Looking for cognitive effects at 2 weeks. Brain creatine equilibrates over weeks-to-months, not days; the trials with effects ran 6 weeks minimum at chronic dose, with the GordjiNejad sleep-deprivation finding being the one rapid-acute exception Gordji-Nejad et al. 2024.
• Wrong form. Anything other than monohydrate is either equivalent at higher cost or actively inferior (ethyl ester).
• Genuine non-response. ~20–30% of users; not preventable.

Practicalities

Cost: bulk creatine monohydrate runs $20–30 for a 1 kg tub (sufficient for ~7 months at 5 g/day) — annual cost under $30. Stability: stable at room temperature for years if dry; degrades to creatinine in solution over days, so pre-mixed liquid products are inferior. Taste: nearly tasteless when dissolved in water or juice. Third-party testing (NSF Certified for Sport, Informed Sport) confirms purity for those concerned about contamination — the supplement industry has periodic quality issues but creatine monohydrate is among the better-policed segments.

Stakes

The substance-absent counterfactual for the typical reader: a 40-year-old on a training programme leaves measurable strength gains (roughly 5–10% additional) and 1–1.5 kg lean mass on the table per year of training, accumulating across a decade Chilibeck et al. 2017. A postmenopausal woman on a training programme loses femoral neck BMD at roughly 3× the rate she would on supplementation Chilibeck et al. 2015. A vegetarian with subclinical low mood may be running on a depleted brain energy substrate that supplementation would correct Rae et al. 2003 Bakian et al. 2020. Magnitude varies by population; the lower-bound case (young omnivore not training) is "miss a small upside"; the upper-bound case (postmenopausal woman on weights, or vegetarian with treatment-resistant depression) is "miss a major one."

Payoff

Timescales for the typical reader on 3–5 g/day:

• Week 1. 1–2 kg weight gain (intramuscular water), muscle-fullness visual effect, no felt energy change Antonio et al. 2021.
• Weeks 2–4. Final set of a hard workout — the one you usually grind through with form breakdown — comes out cleaner; modest endurance increase on the last 1–2 reps of compound lifts Lanhers et al. 2017.
• Months 1–3. Strength numbers diverge from a non-supplementing training partner by ~5–10% on compound lifts. Mood/cognition effects (if present) start to become detectable; the sleep-deprivation buffer becomes available Gordji-Nejad et al. 2024.
• Months 6–12. Additional ~1 kg lean tissue gain over training-alone trajectory Chilibeck et al. 2017. In postmenopausal women on weights, measurable BMD divergence appears at 12 months Chilibeck et al. 2015.
• Years 5–10. Lean-mass and bone trajectories diverge meaningfully — the difference between a 65-year-old who maintained their strength reserves and one who didn't. This is the population-level case for creatine in healthy aging, not formally measured but mechanistically implied by the per-year deltas.

3. The credibility range

The optimist case

Creatine is the most-studied performance supplement in human history (over 1,000 trials, the Kreider et al. 2017 position stand pools many of them), with a multi-dimensional benefit profile no other supplement comes close to matching at the cost. Muscle/strength: settled, ~+1.4 kg lean mass and meaningful strength gains added to resistance training. Bone density: real signal in the most-affected population (postmenopausal women on weights, 70% slower hip-bone loss). Cognition: settled in older adults and under acute stress, increasingly settled in the general population. Mood/depression: small but consistent positive trials with a plausible bioenergetic mechanism that connects to known frontal-cortex phosphocreatine deficits in MDD. Safety: 30 years of trial data and no credible signal of harm in healthy users. Cost: under $30/year. The optimist read is that this is a Pareto-dominant intervention — meaningful effects across 4–5 dimensions, near-zero burden, well-evidenced. The strongest case is that creatine should be a default-recommended supplement for adults over 40 who train, postmenopausal women on weights, vegetarians/vegans, and possibly all adults given the cognitive and bone-aging endpoints.

The skeptic case

The strength evidence is real but modest (SMD 0.265 on upper-body strength is a meaningful but not life-changing effect), and the muscle/lean-mass gains require resistance training to materialise. Without training, what's left is water weight. The cognitive evidence is heterogeneous — null in young omnivores in Sandkühler et al. 2023, equivocal on Raven's matrices, and the Prokopidis 2023 meta-analysis had statistical issues acknowledged by the authors. The depression literature is small, biased toward favourable publication, and the 2025 BJN meta found effects diminish under bias-correction. The bone evidence rests heavily on a single 12-month trial in a single subgroup. Supplement industry incentives ensure ongoing positive coverage and trial funding. Most importantly, creatine's marginal benefit on top of an already-good baseline (training, protein, sleep) is incremental — it should not be confused with foundational interventions. The skeptic read is that creatine is a real but modest add-on whose marketing has gotten ahead of the strongest evidence.

The author's call

Land closer to the optimist case but with calibrated dimension-by-dimension weights. Muscle/strength (≥3 evidence, ≥3 effect on health/longevity via lean mass): settled. Cognition: real signal in older adults and under stress; weaker in young healthy omnivores on chronic dosing. Mood: plausible adjunct, not a primary treatment. Bone: real in postmenopausal women on training. The catalogue position: recommended default for any adult who trains, with stronger recommendation for adults over 40, postmenopausal women on resistance programmes, and plant-based eaters. The intervention's combination of multi-dimensional benefit, near-zero cost and effort, and strong safety profile makes it one of the highest-yield supplements in the catalogue. Evidence rating: 4 (strong on the headline muscle/strength claim; mixed on the secondary claims; the breadth across dimensions does the lifting). Controversy: 1 (mainstream consensus on safety and efficacy; lingering misconceptions are reader-side, not field-side).

4. Stakeholder and incentive map

• Supplement industry (commercial pro-incentive): creatine is among the highest-volume sports supplements; manufacturers (NOW Foods, Optimum Nutrition, Bulk, MyProtein) have a steady commercial interest in adoption. Counter-pressure: monohydrate is generic and cheap, so margins are thin and there's industry pressure to upsell "advanced" forms (HCl, ethyl ester, buffered) at premium pricing despite no efficacy advantage Antonio et al. 2021.
• Sports nutrition academic community (pro-incentive): the ISSN Kreider et al. 2017 position stand authors are aligned with the supplement industry through consulting relationships, an honest declaration in the paper. Their conclusions are broadly corroborated by independent meta-analyses.
• Primary care / nephrology (skeptical-incentive): a generation of physicians trained on the 1998 case-report era of "creatine and kidneys" still occasionally counsels against use; the spurious-creatinine-rise issue creates legitimate friction at routine labs Antonio et al. 2021.
• Online fitness / podcast community (pro-incentive): creatine has become one of the rare supplements with cross-tribal endorsement (Huberman, Attia, Galpin, Israetel) — useful signal that the evidence has converged, but also a category where social proof outruns the cognitive/mood evidence's actual strength.
• Vegetarian/vegan nutrition advocates (pro-incentive): the population-baseline argument for creatine in plant-based diets is well-established and not a contested boundary.

5. Population variability

Strongest responders, ranked by evidence quality:

• Vegetarians and vegans — larger absolute muscle creatine gain from baseline depletion (Burke 2003).
• Adults aged 60+ on resistance training — larger lean-mass gain, plus memory benefit (Chilibeck 2017, Prokopidis 2023).
• Postmenopausal women on resistance training — bone preservation effect specific to this group (Chilibeck 2015).
• Acutely sleep-deprived adults — preserved cognitive performance from acute high dose (Gordji-Nejad 2024).
• Women with MDD on SSRI — augmentation response (Lyoo 2012).
• Children/adolescents post-TBI — outside the catalogue's general-adult scope; flagged for completeness (Sakellaris 2006).

Weakest responders / smallest effect sizes: young omnivore adults not training (effect collapses to early water-weight gain and not much else). The 20–30% non-responder fraction across all populations is real and currently not predictable.

6. Knowledge gaps

• The depression literature needs adequately powered, placebo-controlled, non-augment monotherapy trials. The Eckert 2025 meta-analysis's small effect sizes and high bias signal indicate the current trial set isn't yet definitive.
• The bone density evidence outside postmenopausal women on training is thin. Whether creatine preserves BMD in men, premenopausal women, or non-training older adults remains underexplored.
• Long-term cognitive endpoints (does daily creatine over decades reduce dementia risk?) have no human RCT data. Observational signals exist but are not load-bearing.
• The mechanism of the bipolar manic-switch signal isn't well characterised — n=2 is hypothesis-generating, not definitive, but the biological plausibility is enough to warrant caution.
• The recent finding that vegetarians do not benefit more cognitively than omnivores in Sandkühler et al. 2023 contradicts a long-held assumption and warrants replication.
• What evidence would change the author's call: an adequately powered RCT showing null effects on muscle/strength in trained adults (would downgrade evidence); replicated null trials of depression augmentation (would downgrade mood claim); or a long-term safety signal at common doses (would dramatically downgrade the recommendation). None currently in the literature.

Narrowing relative to the brief. The brief named "muscle, strength, cognition, mood, and bone density." The article covers all five end-to-end, with effect-size and evidence-level honesty per dimension. No silent narrowing. The energy-floor consequence is rolled into cognition (via the sleep-deprivation work) and muscle (via training tolerance) rather than getting its own addressing section — it surfaces as a meta dimension (energy: 2) with a research justification, and is covered in the audience and payoff sections without a dedicated home.

Hard scoring calls.

• evidence: 4 rather than 5 — the headline muscle/strength claim is meta-analytically settled and the trial literature is huge, but the secondary claims (cognition in young omnivores, mood, bone outside the postmenopausal-on-weights subgroup) are heterogeneous enough that 5 would overstate the average across the substance's claimed effects.
• focus: 3 required a judgment call between 2 and 3. The Prokopidis 2023 meta-analysis effect in older adults (SMD 0.88) and the Gordji-Nejad 2024 sleep-deprivation finding push above 2; the Sandkühler 2023 null on vegetarians and the inconsistent young-omnivore results push below 4. Landed at 3 with the dimension dispersed across audience subgroups.
• mood: 2 rather than 3 — the Lyoo 2012 trial and Bakian 2020 NHANES association are real, but the 2025 BJN meta-analysis (Eckert et al.) flagged substantial bias-adjustment effects and very-low certainty. Score reflects real signal, not "clear stabilization."
• longevity: 3 via the sarcopenia and osteoporotic-hip-fracture mechanism, not via any direct mortality endpoint. No human RCT has measured long-term mortality outcomes; the score banks on the well-established mechanism through lean-mass and BMD preservation rather than a direct hazard-ratio.
• beauty_direct: 1 is the early intramuscular-water "fullness" effect — visible to the wearer, generally not to others. Honest 1, not 0.

Contraindications. The closed vocabulary includes kidney-disease but not bipolar. The bipolar caution from Roitman 2007 is real and meets the editorial bar for inclusion, so it is covered in the contraindications addressing section's prose plus warning callout. Future addition of a bipolar token to the meta vocabulary would let this be machine-readable; flagging here for that.

Out of scope, separate-entry candidates.

• Creatine in TBI / neurodegeneration recovery. Sakellaris 2006 pediatric pilot is suggestive; this is a clinical-population entry, not general-adult guidance.
• Loading-phase calculator / per-body-weight dose. The 0.03 g/kg precise dosing covered in passing; could warrant its own short entry if the catalogue grows protocol-detail entries.
• Vegetarian / vegan supplementation stack. Creatine plus B₁₂ plus omega-3 plus iron is a coherent stack worth a top-level entry once the components exist.

Future-link candidates (entries that don't yet exist or weren't linked).

• protein-adequacy — pointed at from out-of-scope.
• resistance-training-basics — pointed at from out-of-scope.
• vitamin-d — pointed at from out-of-scope.
• dexa-scan — pointed at from out-of-scope.
• sleep-debt — implicit related entry given the Gordji-Nejad sleep-deprivation evidence.

Open evidence question worth tracking. Sandkühler 2023 failed to replicate the vegetarian-cognition advantage that Rae 2003 found. The article still cites Rae for vegetarian responsiveness on the muscle side (well-replicated) but is careful in the audience section to flag that the cognitive benefit in vegetarians is now less certain than the early trials suggested. If a future replication disconfirms vegetarian-cognition entirely, the audience-section bullet on vegetarians should be edited to lead with muscle/strength only.