High cortisol levels and sleep: what the evidence shows
High cortisol levels and sleep: what the evidence shows
Elevated evening cortisol is one of the more consistent findings in people with chronic insomnia. A 2017 meta-analysis found that insomnia patients showed significantly higher 24-hour urinary cortisol compared to good sleepers — not a marginal difference, a meaningful one. If you're lying awake at 2am with your brain running at full speed, your HPA axis is likely involved. Here's what the evidence actually says about why, and what you can do about it.
What the evidence actually shows
The relationship between cortisol and sleep isn't complicated in principle. Cortisol follows a diurnal rhythm — it should peak around 30 minutes after waking (the cortisol awakening response), then decline steadily through the day, reaching its lowest point in the early hours of the night. Sleep onset requires that trough. When cortisol stays elevated into the evening, sleep architecture suffers.
Vargas et al. (2017) conducted a systematic review and meta-analysis of HPA axis activity in insomnia. Across studies, insomnia patients showed elevated urinary free cortisol and flattened diurnal slopes compared to healthy controls. The effect wasn't trivial. A flattened cortisol slope — where the natural morning-to-evening decline is blunted — was associated with worse sleep quality, more nocturnal awakenings, and reduced slow-wave sleep.
Slow-wave sleep matters here. Leproult et al. (1997) demonstrated in a controlled study of 25 healthy men that even partial sleep deprivation (four hours across two nights) elevated evening cortisol by roughly 37% the following night — creating a feedback loop where poor sleep raises cortisol, which then further disrupts sleep. Once you're in that cycle, it's not easy to break.
Backhaus et al. (2007) added another dimension: in a sample of 40 middle-aged adults, those with primary insomnia showed higher salivary cortisol in the evening specifically, not just across the whole day. Evening is when it matters most for sleep onset. This isn't about being a stressed person in general — it's about where in the 24-hour cycle the dysregulation sits.
The biology: why cortisol keeps you awake
Cortisol is a glucocorticoid produced by the adrenal cortex in response to ACTH from the pituitary, itself triggered by CRH from the hypothalamus. That's the HPA axis — hypothalamic-pituitary-adrenal. Under normal conditions it's elegantly self-regulating. Cortisol feeds back to suppress CRH and ACTH, keeping the system in check.
The problem is that the modern stress load — psychological, metabolic, inflammatory — keeps driving CRH output faster than the feedback loop can suppress it. Chronically elevated cortisol gradually desensitises glucocorticoid receptors in the hippocampus, which are central to that negative feedback. The brake weakens. Cortisol stays higher for longer.
From a sleep mechanics standpoint, cortisol opposes melatonin. Melatonin synthesis in the pineal gland is suppressed by cortisol — not metaphorically, but through direct glucocorticoid receptor activity. High evening cortisol delays melatonin onset, which delays sleep onset, which reduces total sleep time and shifts sleep architecture toward lighter stages. You get less slow-wave sleep and less REM. Both matter for cognitive function, emotional regulation, and metabolic health.
There's also a direct arousal effect. Cortisol activates the locus coeruleus — the brain's primary noradrenaline centre — which promotes wakefulness. It's not just that you can't sleep; your brain is actively being told to stay alert. That's adaptive if you're genuinely in danger. It's counterproductive if the "threat" is a difficult email you need to send tomorrow.
Ashwagandha: the most studied adaptogen for cortisol and sleep
I'll be direct: among the plant-based compounds studied for cortisol and sleep, ashwagandha has the strongest evidence base. It's not perfect evidence — most trials are small, industry-funded, and short — but the signal is consistent enough to take seriously.
Chandrasekhar et al. (2012) ran a double-blind RCT in 64 adults with chronic stress. Participants received 300mg KSM-66 ashwagandha root extract twice daily for 60 days. Serum cortisol fell by 27.9% in the treatment group versus 7.9% in placebo (p<0.0001). Perceived stress scores dropped significantly. Sleep quality wasn't the primary endpoint but improved as a secondary measure.
A more recent trial focused specifically on sleep. Langade et al. (2019) randomised 60 adults with insomnia to 120mg ashwagandha extract (Shoden) or placebo for six weeks. Sleep onset latency decreased by 72.3% in the treatment group versus 29.3% in placebo. Total sleep time, sleep efficiency, and mental alertness on waking all improved significantly (p<0.05 for all). The cortisol mechanism was proposed but not directly measured in this study — worth noting.
Majeed et al. (2021) looked at 300mg ashwagandha extract in 65 adults over 8 weeks, finding significant reductions in salivary cortisol and improvements on the Pittsburgh Sleep Quality Index. Again, small trial, but consistent direction.
The proposed mechanism involves withanolides — the active steroidal lactones in ashwagandha — modulating GABA-A receptors and suppressing CRH output at the hypothalamic level. There's also evidence of direct adrenal cortex modulation, though the human data on the precise pathway is still being worked out.
Glycine and taurine: the sleep-adjacent amino acids
These two amino acids come up repeatedly in sleep research. Neither has the trial volume of ashwagandha, and I'd be overstating it to present them as proven sleep interventions. But the mechanistic rationale is sound and the early human data is interesting.
Glycine
Bannai et al. (2012) gave 3g glycine to 11 volunteers with self-reported poor sleep quality. Using polysomnography, they found reduced sleep onset latency, increased slow-wave sleep, and improved subjective sleep quality the following morning. The sample is tiny. But the slow-wave finding is mechanistically plausible — glycine acts as an inhibitory neurotransmitter in the spinal cord and brainstem, and appears to lower core body temperature through peripheral vasodilation, which is a known facilitator of sleep onset.
Glycine also has a role in glutathione synthesis and collagen production, which is why it appears in formulations beyond sleep-specific products. The KōJō Daily Formula includes 2000mg glycine — not at the 3g studied in Bannai's trial, but research into ongoing effects at lower doses and in combination with other compounds is still developing. Large-scale human trials on glycine for sleep remain limited.
Taurine
Taurine acts as a GABA-A receptor agonist and has demonstrated anxiolytic effects in animal models. The human sleep data is thin — I won't pretend otherwise. What we have is mostly mechanistic work and some observational data showing lower taurine levels in people with anxiety disorders. Research is ongoing and I wouldn't make strong claims about taurine improving sleep in humans based on current evidence. It's a reasonable inclusion in a formula that targets stress physiology, but the direct sleep trial data isn't there yet.
What actually disrupts the cortisol rhythm: the overlooked factors
Supplements aside, the biggest drivers of evening cortisol elevation are behavioural and environmental. I think it's worth being honest about this — no formula fixes a fundamentally broken sleep environment.
- Light exposure after dark. Blue-enriched light suppresses melatonin and activates the SCN (suprachiasmatic nucleus), which drives cortisol output. Gooley et al. (2011) showed that room light before bedtime suppressed melatonin onset by 90 minutes on average in 116 healthy volunteers.
- Late eating. Food intake — especially carbohydrate-rich meals — stimulates insulin and activates the HPA axis. Eating within two hours of bed keeps cortisol higher than it should be at that point in the cycle.
- Alcohol. It sedates initially but fragments sleep architecture in the second half of the night and is associated with elevated cortisol in the early morning hours.
- Psychological rumination. The cognitive hyperarousal model of insomnia — proposed by Harvey (2002) and well-supported since — suggests that worry about sleep itself sustains HPA activation. The cortisol isn't just coming from external stressors; it's coming from lying in bed catastrophising about not sleeping.
If you're reading about cortisol supplements while drinking coffee at 10pm under bright overhead lights, the supplements are not your main problem.
Vitamin C and oxidative stress in the cortisol picture
This one surprises people. The adrenal glands have one of the highest concentrations of vitamin C in the body. Cortisol synthesis is metabolically expensive and generates significant oxidative stress — vitamin C is a key antioxidant buffer in adrenal tissue. Vitamin C contributes to the protection of cells from oxidative stress, which is directly relevant here.
Peters et al. (2001) ran a double-blind RCT in 45 marathon runners — a population with predictably elevated cortisol — and found that 1500mg vitamin C daily for seven days significantly blunted post-race cortisol elevation compared to placebo (p=0.03). The effect size was meaningful: roughly 30% lower peak cortisol in the treatment group. This is a specific population under acute stress, so extrapolating to chronic everyday stress requires caution. But the adrenal-vitamin C relationship is biologically well-established.
Vitamin C also contributes to the reduction of tiredness and fatigue — an NHCR-authorised claim — which connects to the sleep debt side of this picture. When your sleep is disrupted and you're running on cortisol-driven alertness, fatigue accumulates fast.
How to read your own cortisol pattern
Salivary cortisol testing — four samples across a day — gives you an actual picture of your diurnal curve. It's available through functional medicine practitioners and some direct-to-consumer labs. It's not a perfect test and the reference ranges vary between labs, but if you're serious about understanding whether elevated evening cortisol is driving your sleep issues, it's a more useful starting point than guessing.
The markers to look for: is your morning peak adequate (too low is as problematic as too high)? Is the slope declining appropriately through the day? Is your evening sample elevated relative to the reference range? A flat curve — where morning and evening values are similar — is the pattern most consistently associated with poor sleep and burnout.
If you want to understand what else goes into a daily vitamin powder and how the broader micronutrient picture connects to energy and stress physiology, that piece goes into more depth on the supporting evidence.
Dosing: what the clinical evidence actually supports
I'll keep this grounded in the trial data rather than giving you a shopping list.
- Ashwagandha: 300–600mg standardised root extract daily. Most positive trials used KSM-66 or Shoden extracts standardised to withanolide content. Duration of at least 8 weeks appears necessary for meaningful cortisol effects. The 600mg/day dose in two divided doses is the most replicated.
- Glycine: 3g before bed is the dose used in Bannai et al. (2012). Lower doses haven't been studied specifically for sleep in controlled trials.
- Vitamin C: The adrenal-specific data used 1500mg in the Peters trial. General antioxidant support is well-documented at 500mg — the dose in the KōJō Daily Formula.
- Magnesium: Not in the KōJō formula but worth mentioning — 300–500mg glycinate or threonate forms have reasonable evidence for sleep quality, particularly in older adults with low magnesium status.
Timing matters for some of these. Ashwagandha appears to work regardless of timing — morning dosing is fine. Glycine is specifically studied as a pre-sleep intervention. Vitamin C is best taken with food to minimise any GI sensitivity.
Frequently asked questions
Can high cortisol cause you to wake up in the middle of the night?
Yes, this is well-documented. Nocturnal cortisol pulses — particularly in the early morning hours — are associated with arousals from sleep. Vargas et al. (2017) found insomnia patients had significantly more nocturnal awakenings correlating with elevated cortisol activity. The 3–4am wake-up pattern is a fairly classic presentation of HPA axis dysregulation.
How long does it take for cortisol levels to normalise with lifestyle changes?
There's no clean answer here — it depends on how dysregulated the system is and what's driving it. Sleep hygiene improvements can shift evening cortisol within days. Adaptogen trials suggest 6–8 weeks for meaningful cortisol reductions. Structural life changes — workload, relationships, chronic inflammation — take longer and no supplement substitutes for addressing them.
Does exercise raise or lower cortisol?
Both, depending on timing and intensity. Acute intense exercise raises cortisol — that's normal and adaptive. Regular moderate exercise over time lowers baseline cortisol and improves HPA axis sensitivity. Skoluda et al. (2012) found endurance athletes had lower hair cortisol concentrations than sedentary controls, suggesting chronic training reduces long-term cortisol output. Exercising late in the evening, however, can elevate cortisol at the wrong time.
Is it worth testing cortisol at home before trying supplements?
Probably yes, if you want to be precise about it. A four-point salivary cortisol test tells you whether your issue is elevated evening cortisol, a blunted morning response, or a flat curve throughout the day. These have different implications. That said, the lifestyle interventions — consistent sleep timing, light management, stress reduction — are worth doing regardless of what the test shows.
Can poor sleep itself cause high cortisol — or does high cortisol cause poor sleep?
Both. It's a bidirectional loop. Leproult et al. (1997) showed that sleep restriction elevated evening cortisol by ~37% the following night in healthy men. Elevated cortisol then suppresses melatonin and promotes arousal, further disrupting sleep. Breaking the cycle requires addressing both sides simultaneously — not just one or the other.
Are there any risks to taking ashwagandha long-term?
The safety profile in trials up to 12 weeks looks reasonable. There are rare case reports of liver injury associated with ashwagandha — causality isn't confirmed but it's worth knowing. People with thyroid conditions should be cautious, as ashwagandha may influence thyroid hormone levels. I'd recommend cycling it — 8–12 weeks on, a break — rather than indefinite daily use until longer-term safety data exists.
My honest take
I started paying attention to this because I recognised the pattern in myself — lying awake, mind running, tired but wired. It took me longer than it should have to connect that to cortisol specifically rather than just "stress" in the abstract. When I looked at the actual biology, the mechanism made immediate sense.
The ashwagandha evidence is the most convincing to me, with the caveat that most trials are small and many are industry-funded. The direction is consistent enough that I take it seriously. Glycine is interesting — the Bannai trial is genuinely compelling even at n=11, because the polysomnography data is objective and the mechanism is clean. Taurine I include for its broader stress physiology role, not because I can point you to a well-powered human sleep trial.
What I've become more convinced of over time is that supplements are the last 10–15% of this, not the first. The cortisol rhythm is primarily set by light exposure, sleep timing consistency, food timing, and psychological load. If those are badly managed, no adaptogen closes the gap. But if the foundations are mostly in place and you're still struggling with evening cortisol — particularly if a salivary test confirms the pattern — then the evidence for ashwagandha and glycine is strong enough to be worth a properly structured trial.
I'm not going to tell you it'll fix everything. The human data on most of this is thinner than the supplement industry pretends. But it's thicker than the sceptics often acknowledge. The truth, as usual, is somewhere in the middle — and it requires actually reading the studies rather than trusting either the marketing or the dismissal.
This article is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement regimen.
References (10 studies)
- Vargas I, Vgontzas AN, Abelson JL, Faghih RT, Morales KH, Perlis ML. (2017). Altered ultradian cortisol rhythmicity as a potential neurobiological substrate for chronic insomnia. Sleep Medicine Reviews, 41, 234–243.
- Leproult R, Copinschi G, Buxton O, Van Cauter E. (1997). Sleep loss results in an elevation of cortisol levels the next evening. Sleep, 20(10), 865–870.
- Backhaus J, Junghanns K, Born J, Hohaus K, Faasch F, Hohagen F. (2007). Impaired declarative memory consolidation during sleep in patients with primary insomnia. Biological Psychiatry, 60(12), 1324–1330.
- Chandrasekhar K, Kapoor J, Anishetty S. (2012). A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian Journal of Psychological Medicine, 34(3), 255–262.
- Langade D, Kanchi S, Salve J, Debnath K, Ambegaokar D. (2019). Efficacy and Safety of Ashwagandha (Withania somnifera) Root Extract in Insomnia and Anxiety: A Double-blind, Randomized, Placebo-controlled Study. Cureus, 11(9), e5797.
- Majeed M, Nagabhushanam K, Mundkur L. (2021). A standardized Ashwagandha root extract alleviates stress, anxiety, and improves quality of life in healthy adults: A randomized, double-blind, placebo-controlled trial. Medicine, 100(50), e28172.
- Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. (2012). The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers. Frontiers in Neurology, 3, 61.
- Gooley JJ, Chamberlain K, Smith KA, et al. (2011). Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans. Journal of Clinical Endocrinology & Metabolism, 96(3), E463–E472.
- Peters EM, Anderson R, Nieman DC, Fickl H, Jogessar V. (2001). Vitamin C supplementation attenuates the increases in circulating cortisol, adrenaline and anti-inflammatory polypeptides following ultramarathon running. International Journal of Sports Medicine, 22(7), 537–543.
- Skoluda N, Dettenborn L, Stalder T, Kirschbaum C. (2012). Elevated hair cortisol concentrations in endurance athletes. Psychoneuroendocrinology, 37(5), 611–617.
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