Cortisol and sleeplessness are locked in a two-way relationship that most sleep advice glosses over. Elevated cortisol may disrupt sleep architecture — and disrupted sleep may, in turn, keep cortisol elevated the following morning. One study found that insomnia severity correlated significantly with morning cortisol levels (r = 0.31, p < 0.05) in adults reporting poor psychological health. The loop is real. Breaking it requires understanding the mechanism first.
What the evidence actually shows
The clearest signal in the literature is this: people with clinically defined insomnia tend to show elevated morning cortisol compared with good sleepers. Passos et al. (2023) found that insomnia severity, measured via the Insomnia Severity Index, was positively associated with morning salivary cortisol — and that psychological distress appeared to mediate part of that relationship. The sample was modest (n = 64), so I wouldn't overinterpret the effect size, but the direction is consistent with the broader literature.
Adolescent data adds another angle. Kater et al. (2022) found that sleep disturbances in adolescents were associated with heightened salivary cortisol reactivity to acute stress tasks — suggesting that poor sleep may leave the stress response more reactive, not just more active. Again, causality is hard to establish from cross-sectional data. But the pattern is consistent enough that I take it seriously.
Longer-term cortisol exposure is harder to measure from saliva. Hair cortisol concentration offers a retrospective window — roughly one centimetre of hair per month of exposure. Ahabrach et al. (2023) found that hair cortisol concentration was significantly associated with insomnia symptoms and perceived stress in breast cancer survivors — a population where both stress and sleep disruption are common. The human data on this biomarker is still developing, and I'd be overstating it to call it definitive, but it adds texture to the picture.
If you want a deeper look at the bidirectional nature of this relationship, I've written separately about sleep and cortisol — which covers the hormonal rhythm side in more detail.
The biological mechanism: why cortisol and sleeplessness interact
Cortisol follows a diurnal rhythm governed by the hypothalamic-pituitary-adrenal (HPA) axis. Under normal conditions, cortisol peaks sharply in the 30–45 minutes after waking — a phenomenon called the cortisol awakening response (CAR) — then declines across the day, reaching its nadir around midnight. This rhythm is partly what makes sleep possible: low evening cortisol allows melatonin to rise and core body temperature to fall, both of which are necessary conditions for sleep onset.
When the HPA axis is dysregulated — whether through chronic psychological stress, disrupted circadian signalling, or poor sleep itself — evening cortisol may remain elevated at a time when it should be low. Elder et al. (2014) reviewed the cortisol awakening response in the context of sleep medicine and noted that blunted or exaggerated CAR profiles are associated with various sleep disorders, though the directionality remains complex. Elevated cortisol in the evening essentially signals "alertness" to the brain at precisely the wrong moment.
There's also a metabolic dimension. Van et al. (2009) documented that sleep restriction — even partial, across multiple nights — was associated with alterations in cortisol profiles and appetite-regulating hormones. The neuroendocrine consequences of sleep loss are not trivial, and cortisol is one of the primary mediators. The HPA axis doesn't just respond to psychological stress; it responds to physiological stress too, and insufficient sleep qualifies.
The downstream consequences of chronically elevated cortisol include effects on glucose regulation, cardiovascular function, and mood — all of which can further compound sleep difficulty. Khan et al. (2022) reviewed the cardiovascular consequences of insomnia and sleep loss, noting that the autonomic and neuroendocrine dysregulation associated with poor sleep — cortisol included — may contribute to longer-term cardiovascular risk. This is one reason I don't treat sleep as a soft issue.
The cortisol awakening response: what it tells us about sleep quality
The cortisol awakening response deserves its own section because it's one of the most informative — and most misunderstood — markers in sleep research. The CAR is not simply "morning cortisol". It's the acute surge that occurs in the first 30–45 minutes post-waking, typically representing a 50–160% increase above the immediately post-waking baseline. It's driven by the suprachiasmatic nucleus anticipating the demands of the coming day.
What makes the CAR useful is that it reflects both sleep quality and psychological load. People who sleep poorly — particularly those with fragmented sleep or early-morning waking — tend to show altered CAR profiles. Elder et al. (2014) noted that both blunted and exaggerated CAR responses have been observed in insomnia, depending on the subtype and the presence of comorbid anxiety or depression. A blunted CAR may reflect HPA axis exhaustion; an exaggerated one may reflect hyperarousal.
This matters practically. If you wake feeling unrested despite adequate time in bed, your CAR profile may be part of the story. It's not something most people can measure without a research-grade protocol, but understanding that this morning cortisol surge is sensitive to sleep quality helps explain why a single bad night can leave you feeling wired and exhausted simultaneously — high enough cortisol to feel alert, not enough restorative sleep to feel well.
How sleeplessness perpetuates the cortisol cycle
The most frustrating aspect of the cortisol-sleeplessness relationship is its self-reinforcing nature. Sleep loss may activate the HPA axis, which may keep cortisol elevated, which may make sleep harder — and so the cycle continues. Blake et al. (2019) examined mechanisms linking insomnia with anxiety and depression in adolescents, identifying HPA axis dysregulation as one of the plausible biological pathways. The emotional consequences of poor sleep — irritability, low mood, heightened anxiety — are not just psychological; they have a hormonal substrate.
Ageing adds another layer of complexity. Espiritu (2008) reviewed age-related sleep changes, noting that older adults tend to show earlier circadian phase shifts, more fragmented sleep, and reduced slow-wave sleep — all of which may interact with HPA axis changes that also occur with age. The relationship between cortisol and sleeplessness may therefore become more pronounced as people get older, not less.
I've written more specifically about this feedback loop in my piece on lack of sleep cortisol — if you want to go deeper on what the data says about sleep deprivation's specific effects on cortisol output.
Behavioural and non-supplement approaches with the strongest evidence base
Before talking about anything you can put in your mouth, the evidence base for behavioural intervention is worth acknowledging honestly — because it's stronger than most supplement data.
Cognitive behavioural therapy for insomnia (CBT-I) is the most studied non-pharmacological approach for chronic sleeplessness. Brückner et al. (2025) found that digital CBT-I was effective in nurses with shift work sleep disorder — a population with significant circadian and cortisol disruption — with meaningful reductions in insomnia severity observed across the intervention period. Digital delivery matters because access to trained CBT-I therapists remains limited.
The practical implication: stimulus control, sleep restriction therapy, and cognitive restructuring around sleep-related anxiety all target the hyperarousal that keeps cortisol elevated at night. These are not soft interventions. The effect sizes in CBT-I trials are comparable to, and often exceed, those seen with pharmacological sleep aids — without the dependency risk. If you're dealing with persistent sleeplessness, this is where I'd start before anything else.
What the supplement evidence actually supports for sleep and cortisol
I'll be straight with you: the supplement evidence for cortisol modulation and sleep is thinner than the marketing suggests. Most of the interesting data is either animal-derived, small-sample, or short-duration. That doesn't mean nothing is worth knowing — it means the claims should be proportionate to the evidence.
Magnesium
Khalid et al. (2024) found that magnesium and potassium supplementation was associated with improvements in insomnia scores and sleep hormone profiles in patients with diabetes mellitus — a population with documented sleep disruption. The study was relatively small and specific to a clinical population, so generalising to healthy adults requires caution. The human data on magnesium for sleep in non-clinical populations is mixed, and I'd be overstating it to claim otherwise.
Glycine
Glycine is an amino acid with some preliminary data suggesting it may support sleep onset and sleep quality, possibly via effects on core body temperature regulation. Research is ongoing, and large-scale human trials are limited — so I hold this with appropriate uncertainty. The KōJō Daily Formula includes 2000mg of crystalline glycine, which is in line with the doses used in the available small-scale human studies. Whether it does anything meaningful for cortisol specifically is not something the current evidence supports claiming.
Taurine
Taurine has been studied for its potential role in the nervous system, with some animal data suggesting effects on GABAergic signalling — a pathway relevant to arousal and sleep. The human data is thin, and large-scale trials are limited. I include it in the formula because the safety profile is well-established and the mechanistic rationale is plausible, not because I can point you to a definitive RCT showing it modulates cortisol in humans.
Vitamin C
Vitamin C contributes to the reduction of tiredness and fatigue — that's a registered claim with good mechanistic support. It also contributes to the protection of cells from oxidative stress. Whether oxidative stress plays a role in HPA axis dysregulation is an active area of research, but I wouldn't draw a straight line from "Vitamin C → lower cortisol" based on current evidence. The 500mg in the formula is a reasonable daily dose for general nutritional support.
Polyphenol extracts
Aged Garlic Extract, Olive Leaf Extract, Grape Seed Extract, and Pine Bark Extract are all included in the formula for their potential antioxidant properties. Research is ongoing for each of these, and large-scale human trials examining their specific effects on cortisol or sleep architecture are limited. I include them because the mechanistic rationale is coherent and the safety data is solid — not because I can hand you an RCT showing they fix sleeplessness.
For a related read on how B vitamins interact with this picture, my piece on pyridoxal 5-phosphate vitamin b6 covers the role of B6 in neurotransmitter synthesis — including serotonin pathways that are relevant to sleep regulation.
Frequently asked questions
Does high cortisol directly cause sleeplessness?
The relationship appears bidirectional rather than strictly causal in one direction. Elevated evening cortisol may interfere with sleep onset by maintaining arousal when it should be declining. Equally, poor sleep may keep cortisol elevated the following morning, as documented by Passos et al. (2023). Calling it a simple cause-and-effect relationship would be an oversimplification.
What time of day is cortisol highest, and does that affect sleep?
Cortisol peaks in the 30–45 minutes after waking — the cortisol awakening response — then declines across the day, reaching its lowest point around midnight. This natural rhythm is what permits sleep onset. When the rhythm is disrupted, evening cortisol may remain elevated at a time when it should be low, as reviewed by Elder et al. (2014).
Can a few nights of poor sleep permanently alter cortisol levels?
Probably not permanently — but even short-term sleep restriction may produce measurable neuroendocrine changes. Van et al. (2009) documented alterations in cortisol profiles following partial sleep restriction across multiple nights. Recovery appears possible with adequate sleep, though chronic patterns may be harder to reverse.
Does cortisol-related sleeplessness get worse with age?
The evidence suggests it may. Older adults tend to show earlier circadian phase shifts, more fragmented sleep, and reduced slow-wave sleep, according to Espiritu (2008). Age-related changes in HPA axis regulation may interact with these sleep architecture shifts, potentially making the cortisol-sleeplessness relationship more pronounced over time.
Is CBT-I more effective than supplements for cortisol-related sleeplessness?
For clinically significant insomnia, the evidence base for CBT-I is considerably stronger than for any supplement. Brückner et al. (2025) found digital CBT-I effective even in high-stress shift workers. Supplements may play a supporting role for some people, but they're not a substitute for addressing the behavioural and cognitive drivers of sleeplessness.
Does stress-related insomnia look different from other types of insomnia?
Somewhat. Stress-related insomnia tends to involve difficulty falling asleep and early-morning waking — patterns consistent with HPA axis hyperarousal. Blake et al. (2019) identified HPA dysregulation as a plausible biological pathway linking insomnia with anxiety and depression, suggesting the psychological and physiological components are tightly intertwined rather than separate phenomena.
My honest take
I started looking seriously at cortisol and sleeplessness because I kept waking at 4am with a racing mind — the kind of waking where you feel alert but exhausted simultaneously. That experience maps fairly well onto what the HPA axis literature describes: elevated cortisol at a time when it should be near its nadir, producing arousal without the restorative quality of genuine wakefulness.
What I found when I read the primary literature is that the relationship is real and well-documented, but the solutions are less tidy than most sleep content implies. The evidence for behavioural interventions — particularly CBT-I — is genuinely strong. The evidence for supplements is genuinely mixed. I formulated the KōJō Daily Formula to include ingredients with plausible mechanistic rationale and solid safety profiles, but I try to be honest that "plausible mechanistic rationale" is not the same as "proven to fix your cortisol rhythm".
What I'm more confident about: chronic sleeplessness is not a trivial inconvenience. The cardiovascular, metabolic, and psychological data make that clear. And the cortisol connection is not speculative — it's one of the better-characterised neuroendocrine mechanisms in sleep research. Whether you address it through behavioural change, nutritional support, or both, addressing it at all is worth the effort.
The uncertainty I sit with: we still don't have clean human RCT data showing that specific supplement ingredients meaningfully alter the cortisol-sleeplessness cycle in healthy adults. That gap is real. I'll update my position if the evidence changes.
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)
- Passos et al. (2023) — Insomnia Severity is Associated with Morning Cortisol and Psychological Health. PMID 37151768.
- Kater et al. (2022) — Stress reactivity in salivary cortisol and electrocardiogram in adolescents: Investigating sleep disturbances and insomnia. PMID 35843709.
- Ahabrach et al. (2023) — Hair cortisol concentration associates with insomnia and stress symptoms in breast cancer survivors. PMID 37532197.
- Elder et al. (2014) — The cortisol awakening response — applications and implications for sleep medicine. PMID 23835138.
- Van et al. (2009) — Metabolic consequences of sleep and sleep loss. PMID 18929315.
- Khan et al. (2022) — The Effects of Insomnia and Sleep Loss on Cardiovascular Disease. PMID 35659073.
- Blake et al. (2019) — Mechanisms underlying the association between insomnia, anxiety, and depression in adolescence. PMID 29879564.
- Espiritu (2008) — Aging-related sleep changes. PMID 18035227.
- Khalid et al. (2024) — Effects of magnesium and potassium supplementation on insomnia and sleep hormones in patients with diabetes mellitus. PMID 39534260.
- Brückner et al. (2025) — Effectiveness of digital cognitive behavioral therapy for insomnia in nurses with shift work sleep disorder. PMID 40403587.
