7 Metrics · 28 Supplements

What supplements actually move the numbers on your wearable.

Sleep latency, deep sleep, REM, staying asleep, HRV, resting heart rate, recovery — graded by real evidence, with the funding flags and the popular stuff that doesn't work.

What the evidence says

graded, not marketed

Backed

For at least one metric

No effect

Tested and failed

28 supplements graded across 7 wearable metrics · industry funding flagged on every claim

Wearable metrics

Supplements graded

Backed for a metric

Tested — no effect

The metric-filtered explorer

Pick a metric. See what actually moves it.

Choose the number you stare at every morning, and get the supplements ranked by evidence — what's backed, what's weak, and what's been tested with no effect. Funding flags included.

Choose your metric — 7 to explore

Sleep Latency

Deep Sleep

REM Sleep

Staying Asleep

HRV

Resting HR

Recovery

Recovery / Readiness 15 supplements

Benefit = higher wearable recovery/readiness score (driven by HRV + RHR + sleep vs your baseline).

What's backed

7 supplements · Strong & moderate evidence

Industry-funded

Ashwagandha

Moderate

Lowers cortisol & anxiety, improves sleep; some HRV gain.

Glycine (3 g)

Moderate

Faster onset, better sleep quality; lowers core temperature ~0.28°C.

L-Theanine

Moderate

Lowers HR + cortisol under acute stress; improves sleep.

Industry-funded

Magnesium L-threonate

Moderate

Better deep sleep, REM and readiness scores.

Omega-3 (EPA/DHA)

Moderate

Lowers RHR ~2.2 bpm (DHA, not EPA), which feeds the recovery score; HRV evidence mixed.

Saffron

Moderate

Sleep quality PSQI −2.14 (95% CI −2.86 to −1.42, p<0.01).

Tart Cherry (Montmorency)

Moderate

+34 to 84 min sleep, raises melatonin, eases muscle soreness — double-duty training aid.

Weaker or mixed

4 supplements · Limited or inconsistent

Chamomile (whole extract)

Weak

Improves sleep quality + GAD; NO effect on insomnia (ISI). Use whole extract, not isolated apigenin.

Magnesium (oral)

Weak

Faster onset plus a small readiness / deep-sleep gain on Oura.

Melatonin

Weak

A timing aid, not a recovery booster: 2 mg modestly raises HRV / lowers overnight HR, peaks ~day 3–5 then fades.

Dietary nitrate / beetroot

Mixed

Raises SDNN, lowers sympathetic outflow + BP — acute and population-dependent.

Tested — no effect

4 supplements · Useful nulls

Industry-funded

CBD

No effect

WHOOP data: no meaningful recovery change.

Industry-funded

Creatine

No effect

A cognitive buffer when underslept — not an HRV / recovery aid.

Industry-funded

GABA

No effect

Poor oral absorption — no reliable recovery-score effect.

Valerian

No effect

Subjective improvement only — objective measures unconvincing.

Explore the full Recovery Score Explorer (lifestyle, food & more)

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What the research found: Lowers cortisol & anxiety, improves sleep; some HRV gain.
Study: Witholytin RCT (n=111) + cortisol RCTs.
Evidence grade: Moderate
Funding / quality flag: Proprietary-extract trials; HRV evidence thinner than cortisol.

Source

Ashwagandha (Witholytin) & HRV / cortisol: RCT, n=111 (2023)

Ashwagandha Extract on Amazon

Affiliate link — we may earn a commission. Not an endorsement or medical advice.

What the research found: Faster onset, better sleep quality; lowers core temperature ~0.28°C.
Study: Yamadera 2007 + Inagawa 2006.
Evidence grade: Moderate

Glycine improves sleep quality: PSG evidence (Yamadera 2007)

Glycine Powder on Amazon

What the research found: Lowers HR + cortisol under acute stress; improves sleep.
Study: Kimura 2007.
Evidence grade: Moderate

L-theanine reduces stress responses & improves sleep: RCT

L-Theanine 200mg on Amazon

What the research found: Better deep sleep, REM and readiness scores.
Study: Hausenblas 2024 + Breus 2024.
Evidence grade: Moderate
Funding / quality flag: All manufacturer-funded.

Magnesium L-Threonate on Amazon

What the research found: Lowers RHR ~2.2 bpm (DHA, not EPA), which feeds the recovery score; HRV evidence mixed.
Study: Hidayat 2018 meta, 51 RCTs.
Evidence grade: Moderate

Omega-3 & resting heart rate: 51-RCT meta-analysis (Hidayat 2018)

Omega-3 Fish Oil on Amazon

What the research found: Sleep quality PSQI −2.14 (95% CI −2.86 to −1.42, p<0.01).
Study: Sleep Medicine 2022 meta (PubMed 35325766).
Evidence grade: Moderate

Saffron & sleep quality: meta-analysis (Sleep Medicine 2022)

Saffron Extract on Amazon

What the research found: +34 to 84 min sleep, raises melatonin, eases muscle soreness — double-duty training aid.
Study: Losso 2018 (n=8) + Pigeon 2010 (n=15).
Evidence grade: Moderate

Montmorency tart cherry & sleep: systematic review

Tart Cherry Juice on Amazon

What the research found: Improves sleep quality + GAD; NO effect on insomnia (ISI). Use whole extract, not isolated apigenin.
Study: Phytotherapy Research meta (ptr.6349, 12 RCTs).
Evidence grade: Weak

Chamomile for sleep & anxiety: systematic review & meta-analysis (Phytotherapy Research)

Chamomile Extract on Amazon

What the research found: Faster onset plus a small readiness / deep-sleep gain on Oura.
Study: Mah & Pitre 2021 (n=151) + Breus 2024 Oura (n=31).
Evidence grade: Weak

Magnesium for insomnia: systematic review & meta-analysis (Mah & Pitre 2021)

Magnesium Glycinate on Amazon

What the research found: A timing aid, not a recovery booster: 2 mg modestly raises HRV / lowers overnight HR, peaks ~day 3–5 then fades.
Study: npj Biological Timing & Sleep 2024.
Evidence grade: Weak

Melatonin in the cardiovascular system: dose-dependent effects (npj Biol Timing & Sleep 2024)

Melatonin Supplement on Amazon

What the research found: Raises SDNN, lowers sympathetic outflow + BP — acute and population-dependent.
Study: Notay 2017 (Am J Physiol).
Evidence grade: Mixed

Beetroot nitrate decreases central sympathetic outflow: RCT (Notay 2017)

What the research found: WHOOP data: no meaningful recovery change.
Study: WHOOP cohort analysis.
Evidence grade: No effect (a useful null)
Funding / quality flag: Industry-funded, not peer-reviewed, preclinical, or very small N — read with caution.

What the research found: A cognitive buffer when underslept — not an HRV / recovery aid.
Study: Recovery review; Oura n=21 sleep-duration only.
Evidence grade: No effect (a useful null)
Funding / quality flag: Small / female-only sleep data.

What the research found: Poor oral absorption — no reliable recovery-score effect.
Study: Per recovery-factor review.
Evidence grade: No effect (a useful null)
Funding / quality flag: Industry-funded, not peer-reviewed, preclinical, or very small N — read with caution.

What the research found: Subjective improvement only — objective measures unconvincing.
Study: Shinjyo 2020 meta.
Evidence grade: No effect (a useful null)

Valerian for sleep: systematic review & meta-analysis

Resting HR 11 supplements

Benefit = lower resting heart rate.

What's backed

1 supplement · Strong & moderate evidence

Omega-3 (EPA/DHA)

Strong

Lowers resting HR ~2.23 bpm overall; DHA alone −2.47 bpm, EPA no effect. The only Strong RHR supplement.

Weaker or mixed

3 supplements · Limited or inconsistent

Industry-funded

Chromium

Weak

RHR reduced — but only in metabolic-syndrome / IGT patients.

Oat bran fiber

Weak

24-h heart-rate reduction vs DASH control — hypertensive patients only.

Melatonin

Mixed

Mixed: some lower nocturnal HR; one CAD trial raised 24-h HR. Emerging heart-failure safety signal.

Tested — no effect

7 supplements · Useful nulls

Industry-funded

Ashwagandha

No effect

There is an HRV effect, but no resting-heart-rate change.

Dietary nitrate / beetroot

No effect

No resting-rate change — the effect is autonomic/HRV-side, not a resting-rate drop.

L-Arginine

No effect

No consistent resting-rate change.

L-Theanine

No effect

Acute-stress effect only — not a baseline resting-rate change.

Magnesium (oral)

No effect

No magnesium-specific RHR meta-analysis exists; no reliable resting-rate effect.

Potassium

No effect

+0.2 bpm (95% CI −0.4, 0.8), NS.

Vitamin D

No effect

No heart-rate effect at any dose.

Explore the full Resting Heart Rate Factors (lifestyle, food & more)

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Staying Asleep 8 supplements

Benefit = less wake after sleep onset (lower WASO).

What's backed

3 supplements · Strong & moderate evidence

Industry-funded

Ashwagandha

Strong

WASO SMD −0.39 (3 trials, n=281).

Glycine (3 g)

Moderate

Reduced night-time waking alongside faster SWS onset.

Tart Cherry (Montmorency)

Moderate

Cuts WASO ~17 min vs placebo.

Weaker or mixed

3 supplements · Limited or inconsistent

Magnesium (oral)

Weak

Improves sleep efficiency in the elderly; WASO not directly measured.

Industry-funded

CBD

Mixed

Inconsistent effect on staying asleep.

L-Theanine

Mixed

Mixed WASO results when used alone.

Tested — no effect

2 supplements · Useful nulls

Melatonin

No effect

No significant effect on wake after sleep onset — the most-bought form does NOT aid maintenance.

Valerian

No effect

No consistent objective WASO benefit (subjective only; raised WASO in older women).

Explore the full Staying Asleep Factors (lifestyle, food & more)

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REM Sleep 6 supplements

Benefit = more REM sleep (REM% or REM duration).

REM is the thinnest supplement literature of any metric here, and nothing earns a Strong grade. Watch the measure: Kunz, 5-HTP and glycine are PSG stage data, while the magnesium L-threonate and tart cherry results are Oura scores and Oura minutes, so the numbers are not comparable.

What's backed

2 supplements · Strong & moderate evidence

Industry-funded

Magnesium L-threonate

Moderate

Oura REM Sleep Score rose significantly vs placebo (p<0.05). That is a score, not PSG REM minutes, so read it as "the ring rated REM better", not "you got more REM".

Melatonin

Moderate

Significantly increased REM duration, but only in people whose REM was at least 25% below the age norm. No demonstrated effect in normal sleepers.

Weaker or mixed

2 supplements · Limited or inconsistent

5-HTP

Weak

Raised total REM% at 50 mg/day for 4 weeks, in Parkinson's patients only. Unconfirmed in healthy sleepers, though the serotonin-to-melatonin precursor mechanism is plausible.

Very weak pilot

Tart Cherry (Montmorency)

Weak

REM went 117 to 122 minutes (+5 min) on Oura, taken as tart cherry 800 mg plus magnesium L-threonate 800 mg twice nightly for 30 days. A combination result, not tart cherry alone.

Tested — no effect

2 supplements · Useful nulls

Glycine (3 g)

No effect

No change in REM latency or overall sleep architecture. Useful framing: it speeds sleep onset without disturbing REM, unlike sedatives.

Vitamin B6

No effect

Raises dream recall and dream vividness at 250 mg, but measured sleep variables did not change. Vivid dreams feel like more REM; the trials never showed more REM.

Never tested against this metric

Ashwagandha, valerian, plain magnesium, L-theanine, GABA, saffron, chamomile, tryptophan and CBD have no published REM% on PSG at all. Treat any "boosts REM" claim as unproven unless it cites REM% on PSG.

What actually moves this metric

The clearest REM effects in the literature are suppressors, not supplements. Alcohol pushes REM latency out by about 18 minutes and cuts REM duration by about 11 minutes (at 1 g/kg: +30.1 min latency, −40.4 min duration, REM −2.8 percentage points), and cannabis/THC and nicotine suppress it too.

Explore the full REM Sleep Factor Explorer (lifestyle, food & more)

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Deep Sleep 11 supplements

Benefit = more N3 / slow-wave sleep or delta power.

What's backed

3 supplements · Strong & moderate evidence

Glycine (3 g)

Moderate

Faster slow-wave-sleep onset; stage proportions unchanged.

Industry-funded

Magnesium L-threonate

Moderate

Raises deep sleep, REM and readiness on Oura.

Melatonin

Moderate

MT2 activation in the reticular thalamus raises NREM + delta power.

Weaker or mixed

7 supplements · Limited or inconsistent

Industry-funded

Ashwagandha

Weak

Raises delta power + GABA-A expression — in vitro / animal only.

L-Theanine

Weak

Raises delta and reverses caffeine’s delta suppression — animal ECoG model.

Magnesium (oral)

Weak

Slow-wave sleep ~+6 min; raises delta + sigma power — in older adults.

Omega-3 (EPA/DHA)

Weak

Improves sleep efficiency (+1.88 pp pooled); no isolated deep-sleep (N3) gain.

Industry-funded

Passionflower

Weak

Raises self-reported total sleep time; no PSG, N3 never measured.

Industry-funded

PeptiSleep

Weak

Claimed deep-sleep gain — manufacturer data only.

Tart Cherry (Montmorency)

Weak

+84 min total sleep time on PSG (p=0.0182).

Tested — no effect

1 supplement · Useful nulls

Vitamin D

No effect

Supplementation gives no clear deep-sleep (N3) gain; subjective PSQI only.

Explore the full Deep Sleep Factor Explorer (lifestyle, food & more)

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Sleep Latency 12 supplements

Benefit = you fall asleep faster (shorter sleep onset).

What's backed

6 supplements · Strong & moderate evidence

Industry-funded

Ashwagandha

Strong

Sleep onset SMD −0.53 (p<0.001); 600 mg most effective.

Melatonin

Strong

Sleep onset −7.06 min (p<0.001); peaks around 4 mg.

Industry-funded

GABA

Moderate

Sleep onset 13.4 → 5.7 min (p=0.001).

Glycine (3 g)

Moderate

Shortened sleep onset and slow-wave-sleep latency (p=0.01).

L-Theanine

Moderate

Subjective sleep onset SMD 0.15 (p=0.04); no objective effect.

Magnesium (oral)

Moderate

Sleep onset ~17 min faster (−17.36 min, p=0.0006).

Weaker or mixed

3 supplements · Limited or inconsistent

5-HTP

Weak

Possible faster onset — only tiny RCTs.

Industry-funded

PeptiSleep

Weak

Claimed faster onset — manufacturer data only.

Tryptophan (≥1 g)

Weak

Shortens sleep onset in older trials.

Tested — no effect

3 supplements · Useful nulls

Industry-funded

CBD

No effect

CBD isolate 150 mg: no effect on sleep onset.

Tart Cherry (Montmorency)

No effect

No sleep-onset benefit.

Valerian

No effect

Pooled sleep-onset difference 0.70 min (NS).

Explore the full Sleep Latency Factors (lifestyle, food & more)

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HRV 12 supplements

Benefit = higher HRV (RMSSD / HF power).

What's backed

8 supplements · Strong & moderate evidence

Industry-funded

Ashwagandha

Strong

RMSSD rose vs a decline in placebo (time×group p=0.003).

Omega-3 (EPA/DHA)

Strong

Consistently raises HF power — the most-studied dietary HRV factor.

Industry-funded

GABA

Moderate

Raises HRV via parasympathetic predominance.

L-Theanine

Moderate

Attenuates sympathetic activation during acute stress.

Industry-funded

Magnesium L-threonate

Moderate

RMSSD +1.45 ms, RHR −1.32 bpm (p=0.036 / 0.030) on Oura.

Multivitamin

Moderate

One RCT prevented HRV decline — a buffer, not a booster.

Vitamin B12

Moderate

Deficiency reduces LF power (correction effect in deficiency).

Vitamin D

Moderate

Deficiency is associated with lower HRV (a deficiency-correction effect, not a booster).

Weaker or mixed

4 supplements · Limited or inconsistent

Industry-funded

PeptiSleep

Weak

+32% HRV claim (Oura).

Zinc

Weak

Prenatal zinc linked to better offspring HRV; adult data limited.

Dietary nitrate / beetroot

Mixed

Raises SDNN acutely; lowers sympathetic outflow.

Magnesium (oral)

Mixed

One small RCT showed an increase (n=36); results vary by form — hype is ahead of the data.

Explore the full HRV Factor Explorer (lifestyle, food & more)

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The research says maybe. Your data says yes or no.

Evidence is population-level. Kygo tracks what a supplement does to your own sleep, HRV and recovery numbers.

Works with

Oura

Apple

Fitbit

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WHOOP

Polar

Google

Health

The master matrix

Every supplement, every metric, at a glance.

One grade per cell: how good the evidence is that this supplement moves that metric in the right direction. Ranked strongest-overall first.

Evidence grades

Supplement × metric, graded by evidence

Blank = no metric-specific evidence found. Use the explorer above to read the studies behind any cell.

28 supplements · 7 metrics

Supplement	Latency	Deep	REM	WASO	HRV	RHR	Recovery
Ashwagandha	S	W	–	S	S	✗	M
Melatonin	S	M	M	✗	–	~	W
Omega-3 (EPA/DHA)	–	W	–	–	S	S	M
Glycine (3 g)	M	M	✗	M	–	–	M
L-Theanine	M	W	–	~	M	✗	M
Magnesium L-threonate	–	M	M	–	M	–	M
Magnesium (oral)	M	W	–	W	~	✗	W
Tart Cherry (Montmorency)	✗	W	W	M	–	–	M
GABA	M	–	–	–	M	–	✗
PeptiSleep	W	W	–	–	W	–	–
5-HTP	W	–	W	–	–	–	–
Multivitamin	–	–	–	–	M	–	–
Saffron	–	–	–	–	–	–	M
Vitamin B12	–	–	–	–	M	–	–
Vitamin D	–	✗	–	–	M	✗	–
Chamomile (whole extract)	–	–	–	–	–	–	W
Chromium	–	–	–	–	–	W	–
Dietary nitrate / beetroot	–	–	–	–	~	✗	~
Oat bran fiber	–	–	–	–	–	W	–
Passionflower	–	W	–	–	–	–	–
Tryptophan (≥1 g)	W	–	–	–	–	–	–
Zinc	–	–	–	–	W	–	–
CBD	✗	–	–	~	–	–	✗
Creatine	–	–	–	–	–	–	✗
L-Arginine	–	–	–	–	–	✗	–
Potassium	–	–	–	–	–	✗	–
Valerian	✗	–	–	✗	–	–	✗
Vitamin B6	–	–	✗	–	–	–	–

Strong

Moderate

Weak

Mixed

✗

Tested, no effect

Funding flag

The honesty layer

The popular stuff that doesn't work.

Magnesium's "27 RCTs"

3 trials

Really just n=151

The viral "27 RCTs / 2,496 people" figure is actually 3 small trials totalling 151 older adults, rated low-quality. Magnesium does help sleep onset — just nowhere near the marketing number.

Melatonin & staying asleep

No effect

It won't keep you asleep

Standard immediate-release melatonin shows no significant effect on wake after sleep onset (Moon 2022). It's a timing aid for falling asleep, not a maintenance aid.

CBD & recovery

No change

WHOOP saw nothing

CBD shows no meaningful recovery change on WHOOP, and CBD isolate 150 mg was null for sleep onset (Narayan 2024). Don't rely on it for your score.

Apigenin (the trendy one)

0 RCTs

No human sleep trial exists

Isolated apigenin — the trendy ~50 mg version — has zero human sleep RCTs. The evidence people cite is for whole chamomile extract. Use the extract, not the isolate.

Passionflower

Subjective

Self-report, industry-funded

The "evidence" was self-reported total sleep time with no PSG, in an industry-funded trial (JK Botanicals). Deep sleep was never actually measured.

L-theanine & resting HRV

Acute only

Not a baseline gain

L-theanine blunts sympathetic activation during acute stress (Kimura 2007) — it is not a resting-HRV or baseline resting-heart-rate improvement.

Vitamin B6 & "more REM"

Dreams only

Vivid, not longer

B6 raises dream recall and vividness (Ebben 2002, Aspy 2018), but measured sleep variables did not change. Remembering more dreams feels like more REM. It is not the same thing.

Supplements that "boost REM"

9 untested

No PSG data at all

Ashwagandha, valerian, plain magnesium, L-theanine, GABA, saffron, chamomile, tryptophan and CBD have never been measured for REM% on PSG. The honest grade for REM is usually "not tested", not "works".

Read this before you buy anything

Frame every row as "research shows X affects this metric," never "take X to fix your number." Many of these effect sizes — RHR −2.2 bpm, HRV +1.45 ms — are small next to a wearable's night-to-night noise, and most were measured on Oura specifically (see how accurate your wearable is and the sensor comparison). Nearly every supplement-specific trial here is industry-funded. Doses are study doses, not recommendations. This is not medical advice — talk to a clinician before changing your routine.

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38 research-backed factors that affect Heart Rate Variability, ranked by evidence.

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REM Sleep Factor Explorer

37 research-backed factors that raise, lower or don't change REM sleep, with mechanisms.

Sleep · 37 factors

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Common questions

Supplements & your metrics, answered.

Which supplements are actually backed for wearable metrics?

The defensible ones, by evidence: omega-3 (resting heart rate −2.23 bpm and HRV), ashwagandha (sleep latency, staying asleep and HRV — though the trials are industry-funded), glycine 3 g (latency, deep sleep and staying asleep), magnesium (latency ~17 min faster), saffron (sleep quality, PSQI −2.14), and tart cherry (less waking, recovery). L-theanine helps HRV under acute stress, and melatonin speeds sleep onset by about 7 minutes. Everything else is weaker, mixed, or tested-with-no-effect. Doses cited are study doses, not recommendations, and this is not medical advice.

Do any supplements actually increase REM sleep?

Barely, and nothing earns a Strong grade. Melatonin significantly increased REM duration in two randomized PSG trials, but only in people whose REM was at least 25% below the age norm (Kunz 2004, n=14), with no demonstrated effect in normal sleepers. Magnesium L-threonate raised the Oura REM Sleep Score versus placebo in a 21-day RCT (Hausenblas 2024, n=80), though that is a ring score rather than PSG REM minutes and the trial was funded by the Magtein distributor. 5-HTP raised REM% at 50 mg over 4 weeks in Parkinson's patients only. Everything else is weaker: a tart cherry plus magnesium L-threonate pilot found REM going 117 to 122 minutes on Oura in 7 people with no placebo. Glycine is a useful null, speeding sleep onset without disturbing REM. Ashwagandha, valerian, plain magnesium, L-theanine, GABA, saffron, chamomile, tryptophan and CBD have never had REM% measured on PSG, so treat any "boosts REM" claim as unproven unless it cites REM% on PSG. Not medical advice.

Does vitamin B6 give you more REM sleep?

No. B6 at 250 mg raises dream recall and dream vividness (Ebben 2002, Aspy 2018), but measured sleep variables, including REM, did not significantly change. Remembering more dreams feels like more REM sleep, which is why the claim spreads, but the trials never showed a longer REM stage. If your wearable shows more REM on a B6 night, that is far more likely to be night-to-night noise in the device estimate.

What actually reduces REM sleep?

The clearest REM effects in the literature come from suppressors, not supplements. A 27-study meta-analysis found alcohol pushed REM latency out by about 18 minutes and cut REM duration by about 11 minutes, and at 1 g/kg the effect grew to +30.1 minutes of latency, −40.4 minutes of duration and a 2.8 percentage-point drop in REM% (Gardiner 2024). Cannabis/THC and nicotine suppress REM as well. Removing a suppressor is a far bigger lever on your REM number than adding any supplement in this matrix.

What is the biggest supplement myth here?

The magnesium "27 RCTs / 2,496 people" figure that circulates on blogs. The actual meta-analysis (Mah & Pitre 2021) is just 3 small trials totalling 151 older adults, rated low-quality evidence. Magnesium does help sleep onset modestly — but nowhere near as strongly as the marketing number implies.

Does melatonin help you stay asleep?

No. Standard immediate-release melatonin — the most-bought form — shows no significant effect on wake after sleep onset (WASO) in meta-analysis (Moon 2022). Melatonin is a circadian timing aid that helps you fall asleep faster (about 7 minutes), not a sleep-maintenance aid. For staying asleep, the better-supported options are ashwagandha, tart cherry and glycine.

What actually lowers resting heart rate (RHR)?

Omega-3 is the only supplement with strong RHR evidence: roughly −2.23 bpm overall, and −2.47 bpm for DHA specifically (EPA alone does nothing), across a 51-RCT meta-analysis. Potassium, vitamin D, L-arginine and dietary nitrate all came out null for resting heart rate. Chromium and oat-bran fiber only helped in specific patient groups.

What raises HRV?

Omega-3 (raises HF power — the most-studied dietary HRV factor) and ashwagandha (RMSSD rose vs a placebo decline, though it is a single proprietary-extract trial). GABA and magnesium L-threonate have moderate but industry-funded evidence. L-theanine helps during acute stress but is not a resting-HRV gain, and the magnesium-for-HRV story is hype ahead of the data.

Can I trust these supplement studies — who funds them?

Be skeptical. Nearly every supplement-specific RCT in this data is industry-funded, including every magnesium L-threonate, ashwagandha and PeptiSleep trial — they are flagged with a funding marker throughout. Industry funding does not automatically make a result wrong, but independent replication is the single biggest evidence gap across the whole category. Saying so openly is the point.

Will a supplement noticeably change the number on my ring or watch?

Maybe not visibly. Many of these effect sizes — RHR −2.2 bpm, HRV +1.45 ms — are small relative to a wearable's night-to-night noise, and most were measured on Oura specifically. Read every claim as "research shows X affects this metric," never "take X to fix your number." Pair any change with the device-detectability caveat and check our wearable-accuracy tools.

What about saffron and chamomile for recovery?

Saffron is surprisingly solid for a botanical — a meaningful sleep-quality improvement (PSQI −2.14) across a large meta-analysis. Whole-extract chamomile improves sleep quality and anxiety but does NOT fix clinical insomnia, and the trendy isolated apigenin version has zero human sleep RCTs — so use whole extract if you use it at all.

Sources

Every supplement claim verified against primary research (2026-06-12 pass, REM sleep added 2026-08-19). Funding flags are part of the data — they travel with each claim.