Can high cortisol cause insomnia?

Yes — and the evidence is reasonably consistent on this. Elevated evening cortisol appears to be one of the more plausible physiological drivers of sleep-onset difficulty. In one study of older adults, higher nocturnal cortisol was directly associated with worse sleep quality and more frequent night waking. The mechanism is not mysterious: cortisol is an arousal hormone, and arousal is the enemy of sleep onset.

What the evidence actually shows

The relationship between cortisol and poor sleep has been studied from several angles. The clearest signal comes from populations where cortisol dysregulation is most pronounced — older adults, people under chronic stress, and clinical cases of cortisol excess.

Castello-Domenech et al. (2017) looked at cortisol levels in non-demented older individuals and found that higher nocturnal cortisol was associated with significantly disrupted sleep architecture — specifically reduced slow-wave sleep and more frequent arousals. This matters because slow-wave sleep is the stage most associated with physical recovery. Lose it, and you feel it.

In adolescents, Kater et al. (2022) examined salivary cortisol reactivity and its relationship to sleep disturbances and insomnia symptoms. They found that heightened cortisol stress reactivity was associated with greater sleep problems — though the authors were careful to note that causality is hard to establish in cross-sectional designs. I appreciate that kind of methodological honesty. It's a correlation that makes biological sense, but "makes sense" is not the same as "proven".

On the neuroendocrine side, von et al. (2019) found that sleep problems were associated with measurably altered neuroendocrine hormone profiles in patients recovering from acute cardiac events — a population where the HPA axis is already under significant strain. That's a specific clinical context, not a general population finding, and I'd be overstating it to apply it universally. But it adds to the picture.

If you want a deeper look at the broader cortisol-sleep relationship, I've written separately about cortisol and sleeplessness — that piece goes further into the neuroendocrine literature.

The mechanism: what's actually happening in your body

Cortisol is produced by the adrenal cortex in response to signals from the hypothalamic-pituitary-adrenal (HPA) axis. Under normal circumstances, cortisol follows a tight diurnal rhythm: it peaks sharply within 30–45 minutes of waking — the cortisol awakening response — and then declines steadily throughout the day, reaching its lowest point in the hours around midnight.

That evening nadir is not incidental. It's what allows melatonin to rise and the brain to shift into sleep mode. When cortisol remains elevated into the evening — whether from chronic psychological stress, disrupted light exposure, irregular sleep timing, or HPA axis dysregulation — it effectively competes with that transition.

Elder et al. (2023) describe how chronic stress leads to sustained HPA axis activation, with downstream effects on sleep architecture and circadian timing. The pathway runs roughly like this: perceived threat activates the hypothalamus → corticotropin-releasing hormone (CRH) is released → the pituitary releases ACTH → the adrenal glands produce cortisol. In acute stress, this system is self-limiting. In chronic stress, the negative feedback loop may become dysregulated, and evening cortisol stays elevated when it should be falling.

There's also a reciprocal relationship worth noting. Hansen et al. (2021) found that sleep deprivation and sleep-onset insomnia were associated with blunted physiological reactivity to subsequent stressors — suggesting that poor sleep and HPA dysregulation may reinforce each other in a bidirectional loop. In other words, high cortisol may contribute to insomnia, and insomnia may then further dysregulate the cortisol response. That's a frustrating cycle if you're stuck in it.

Cortisol also has direct excitatory effects on the central nervous system. It increases noradrenaline activity, raises core body temperature slightly, and promotes wakefulness via interactions with the locus coeruleus. None of those effects are conducive to sleep onset. The body is, essentially, being told to stay alert at the precise moment it needs to wind down.

Clinical extremes: what Cushing's syndrome tells us

The most dramatic illustration of what sustained cortisol excess does to sleep comes from clinical conditions involving pathological cortisol overproduction.

Elston et al. (2022) documented a case of severe Cushing's syndrome — a condition characterised by chronically elevated cortisol — and noted that sleep disturbance was among the prominent symptoms. Cushing's is rare, and I'm not suggesting everyone with poor sleep has it. But it provides a useful proof of concept: when cortisol is persistently and pathologically high, sleep is reliably disrupted.

This is clinically distinct from the kind of cortisol elevation most people experience from work stress or poor sleep habits. But the underlying mechanism — elevated arousal signalling at night — is the same, just on a different scale.

For a more detailed breakdown of the symptom picture, my piece on high cortisol symptoms sleep covers the broader clinical presentation beyond just insomnia.

The age factor: why older adults are particularly affected

Cortisol's relationship with sleep appears to worsen with age. There are two reasons for this. First, the HPA axis becomes less tightly regulated as we get older — the negative feedback that normally dampens cortisol after a stressor becomes less efficient. Second, sleep architecture itself changes with age: slow-wave sleep declines naturally, and sleep becomes more fragmented.

The data from Castello-Domenech et al. (2017) is particularly relevant here. Their work in non-demented older adults found that nocturnal cortisol levels were a meaningful predictor of sleep quality — specifically that higher cortisol was associated with reduced total sleep time and more arousals. The sample was community-dwelling adults rather than a clinical population, which makes it more applicable to everyday experience.

This also has implications for long-term mental health. Zagaria et al. (2024) found that insomnia symptoms were long-term predictors of anxiety in middle-aged and older adults — a reminder that disrupted sleep is rarely just a sleep problem. It tends to compound.

Circadian timing: it's not just how much cortisol, it's when

Something I find underappreciated in popular discussions of this topic: the timing of cortisol elevation matters as much as the absolute level. A morning cortisol spike is normal and healthy. The same spike at 11pm is a problem.

Moon et al. (2022) examined how circadian rhythm disruption — specifically alterations in the timing of hormonal peaks — affects sleep quality. Their systematic review found that circadian misalignment had measurable effects on sleep architecture across multiple populations. The cortisol-melatonin relationship is particularly sensitive to this: when cortisol's evening decline is delayed, melatonin's rise is also delayed, pushing the entire sleep-onset window later.

This is one reason why late-night screen exposure, shift work, and irregular meal timing can all contribute to sleep problems even in people who aren't experiencing obvious psychological stress. They disrupt the circadian cues that tell the HPA axis when to stand down.

For more on the specific insomnia presentation associated with this pattern, the piece on high cortisol insomnia goes into the clinical detail.

What the data suggests about nutritional approaches

I want to be careful here. There's no supplement that will directly fix a dysregulated HPA axis, and I'd be doing you a disservice to imply otherwise. What I can do is point to where the evidence is at least interesting, and be honest about where it's thin.

Glycine has been studied in the context of sleep quality in small human trials, with some preliminary data suggesting it may support sleep onset when taken before bed. Research is ongoing, and large-scale human trials are limited — I wouldn't stake a strong claim on this yet. The KōJō Daily Formula includes 2000mg of crystalline glycine, partly because the safety profile is well-established and the early sleep data is at least plausible.

Taurine has been studied for its potential interactions with the GABAergic system, which is relevant to sleep and anxiety. The human data on this is thin and I'd be overstating it to claim taurine directly addresses cortisol-related insomnia. Research is ongoing, and large-scale human trials are limited.

Vitamin C is worth mentioning in a different context. Vitamin C contributes to the reduction of tiredness and fatigue, and contributes to the protection of cells from oxidative stress — both registered claims. Oxidative stress is elevated during periods of chronic stress, so adequate Vitamin C status is at least sensible. The formula includes 500mg.

Aged Garlic Extract, Olive Leaf Extract, Grape Seed Extract, and Pine Bark Extract are all included in the formula for their antioxidant and cardiovascular-adjacent properties. None of them have strong direct evidence for cortisol or sleep specifically in large-scale human trials — research is ongoing across all four, and I won't overstate what the current data supports.

Practical signals that cortisol timing might be the issue

Not all insomnia is cortisol-driven. But there are patterns that suggest HPA timing is a likely contributor rather than something else:

• You feel genuinely tired in the evening but become alert when you get into bed
• Your mind races at night with thoughts that feel urgent or anxious
• You wake between 2am and 4am feeling alert rather than groggy
• You feel better after a lie-in, suggesting your cortisol awakening response is simply shifted later
• Stress levels during the day are high, and evenings don't feel like genuine wind-down time

These are not diagnostic criteria. They're patterns. But they're useful for thinking about whether the cortisol-sleep axis is worth paying attention to in your specific situation.

Frequently asked questions

My honest take

I started paying attention to this topic because I noticed a pattern in myself. Busy periods at work — the kind where my brain is still running problem-solving loops at 11pm — reliably produced nights where I'd lie awake for an hour before sleep arrived. I'd always assumed that was psychological. Reading the HPA literature made me think it's probably both: psychological stress activates a physiological response, and that physiological response is the actual proximate reason sleep doesn't come.

That distinction matters to me. Not because it changes what you do about it — wind-down routines, consistent sleep timing, limiting evening light exposure are sensible regardless — but because it makes the problem feel less like a personal failing and more like a biological mechanism that can be worked with.

The supplement angle is where I try to stay honest with myself. Glycine and taurine are in the KōJō formula partly because the early sleep-adjacent data is interesting. But I'm not going to tell you they'll fix a cortisol problem. The evidence isn't there yet at the scale I'd need to make that claim confidently. What I can say is that the safety profiles are solid, the doses are meaningful, and the research is active.

The bigger levers — the ones with the strongest evidence — are behavioural. Consistent wake time. Evening light management. Reducing late-night cognitive load. None of that is exciting to write about, but it's where the effect sizes are largest. Supplements sit alongside that, not instead of it.

If your sleep is seriously disrupted and you suspect a cortisol component, testing is worth considering before spending money on anything. A basic diurnal salivary cortisol panel will tell you more than any supplement label.

This article is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement regimen.