Bloodwork

Cortisol

The Stress Axis

22 formulas on this site modulate this pathway.

Acute vs chronic: a cortisol pulse is how you meet a demand and it is why the rhythm exists. It is the sustained elevation that costs you sleep, mood, hair and a sound gut barrier. You want it down from a smouldering baseline, not down from zero. Cortisol in rhythm energizes and repairs; cortisol without rest wears down mood, memory and metabolism. Balance is the goal.

What this marker reads

The hypothalamic–pituitary–adrenal axis and its hormone cortisol — the body's central stress-and-recovery command.

No body publishes a range for this marker

No named body publishes a reference interval for morning serum cortisol. The guideline gives adrenal-insufficiency cut-points only, marks them assay dependent, and calls the rule-out values controversial — the assay-specific low limit alone spans 418–574 nmol/L.

Your laboratory reads your result against its own assay, and this page does not do that for it. What is above is what a named body published and for whom; what is below is the machinery the marker reads and the formulas witnessed on it.

What moves it

Gut barrier lowers it.

The microbiota-gut-brain axis regulates HPA activity in humans: in a randomized placebo-controlled trial, Bifidobacterium breve CCFM1025 significantly lowered PSQI scores in stress-induced insomnia and produced a more pronounced reduction in stress-marker concentrations (PMC10648101); a second RCT targeted the same melatonin/HPA route (PMC12787598). Convergent, and the founding evidence is a loss-of-function model: germ-free mice show exaggerated stress responses (Sudo 2004) — absence of microbiota alters HPA reactivity. Mechanistically, gut dysbiosis produces pro-inflammatory cytokines and microbial antigens that activate the HPA axis across the blood-brain barrier, and microbiota-host interaction releases cytokines that disrupt the BBB itself. The reviews note HPA overactivation is one cause of depression — one among several, not the account. Shared caveats on this whole row: (1) the route to the brain is not free — gut-derived neurotransmitters reach targets via the bloodstream and must cross the blood-brain barrier; elevated plasma 5-HT can itself raise BBB permeability, temporarily letting plasma 5-HT enter the CNS, so the barrier is a variable not a constant. (2) much of this literature is association — the reviews state plainly that the association studies linking microbiota to depression did not provide evidence on aetiology. (3) The enteric nervous system hosts more than 30 neurotransmitters; any single arrow is one strand of a dense web. PMC10648101

Stress-relapse axis raises it.

Vale 1981, Science 213:1394 — the 41-residue CRF peptide that drives pituitary ACTH secretion (→ cortisol). DOI 10.1126/science.6267699 Verbatim: “CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary”. doi 10.1126/science.6267699 · PMID 34830130

Body clock raises it.

Reverse ARROWThe atlas drew only the HPA Axis / Cortisol → Circadian Rhythm link, the weaker leg. The lesion evidence is definitive: loss of the circadian rhythm of corticosterone after suprachiasmatic nucleus lesions provided some of the first evidence that the SCN is the brain's master clock; ablating SPZ-Vgat neurons eliminates the circadian rhythm of corticosterone secretion; and the SCN is required for the daily rhythm of plasma glucocorticoids (PMC11261983; PMC3718825). Photic activation of the SCN raises plasma glucocorticoids. Route: SCN -> subparaventricular zone -> dorsomedial hypothalamus -> PVH CRH neurons, plus rhythmic SCN vasopressin, plus a splanchnic nerve line direct to the adrenal. Control is bimodal, not one-way: the adrenal has its own intrinsic clock driving cyclic steroidogenesis. Daytime restricted feeding uncouples the two and produces two separate glucocorticoid peaks — one tied to adrenal content, one requiring an intact SCN. And photic SCN activation raised glucocorticoids without a functional adrenal molecular clock, so part of the pathway is ACTH-independent and neural (Sci Rep 2017;7:46404 / PMC5388859). Species: rat and mouse. PMC11261983

Pituitary stress signal raises it.

NBK500031 — ACTH released from the anterior pituitary acts on the adrenal cortex to promote glucocorticoid synthesis and release — primarily cortisol in humans. Glucocorticoids then exert negative feedback on both hypothalamus and pituitary, inhibiting further crh and acth. The feedback wears out, which is the clinically important part: this feedback is transcriptional, via glucocorticoid receptors, and chronic glucocorticoid exposure decreases receptor expression, resulting in reduced negative feedback. Sustained stress degrades its own off-switch.

The Two-Faced Peptide raises it.

the human data is the strong part: stress induces dynorphin release, and activation of KORs with a synthetic agonist increases corticosterone in rats and cortisol levels in rhesus monkeys and humans. KORs are expressed in the organs of the HPA axis as well as the brain regions that regulate it. The mechanism is explicitly unsettled and that is recorded: it likely involves stimulation of CRF release in the hypothalamus as well as CRF-independent mechanisms — so this arrow does not run wholly through crf. The return path is disinhibition — KOR activation in the central amygdala presynaptically inhibits the FEEDFORWARD inhibition driven by glutamatergic parabrachial input, thereby disinhibiting CeA CRF neurons. Each peptide recruits the other, by opposite mechanisms. And they compete in the same synapse: exogenous CRF raised GABAergic mIPSC frequency by 20.2 percent, and while norBNI alone had no significant effect, it enhanced the CRF effect by 43.9 percent (P=0.02) — blocking KOR makes CRF stronger, because CRF was recruiting an opposing KOR arm all along. doi 10.1016/j.neuropharm.2021.108456 · PMC3770816

Sleep hormone lowers it.

melatonin also suppresses GR nuclear translocation by maintaining the GR in a complex with heat shock protein 90; melatonin, directly and/or epigenetically, can upregulate BAG-1. PMC10645470

Social engagement lowers it.

Placebo-controlled double-blind trial, 37 healthy men, Trier Social Stress Test: salivary free cortisol was suppressed by social support in response to stress. Heinrichs 2003, Biol Psychiatry 54:1389 — Social support and oxytocin interact to suppress cortisol and subjective responses to psychosocial stress. doi 10.1016/S0006-3223(03

Social bonding hormone lowers it.

Intranasal oxytocin before the Trier Social Stress Test was anxiolytic, and oxytocin combined with social support produced the lowest cortisol concentrations of any arm. Heinrichs 2003, Biol Psychiatry 54:1389 — Social support and oxytocin interact to suppress cortisol and subjective responses to psychosocial stress. doi 10.1016/S0006-3223(03

Trauma symptoms raises it.

Stress-induced extinction impairments contribute to relapse of fear in patients undergoing exposure therapy; the HPA axis is named as a system altering fear extinction through BDNF modulation. doi 10.1111/j.1601-183X.2012.00801.x · PMC2787650

Mood lowers it.

10.1038/s41398-024-03210-5 — Flattened cortisol diurnal slopes are linked to poorer emotional and physical health such as cardiovascular diseases in a meta-analysis of 80 studies across all ages ranging from children to older adults. doi 10.1038/s41398-024-03210-5 · PMC4880118

What it moves

It lowers Sleep.

HPA hyperactivity and disturbed sleep travel together: insomnia, depression, Cushing’s syndrome and sleep-disordered breathing all display HPA hyperactivity alongside disrupted sleep (PMC2902103), and elevated cortisol presents clinically as insomnia. Verified: loss of physiological cortisol suppression — elevated morning and bedtime cortisol — is linked to reduced hippocampal feedback sensitivity to glucocorticoids and leads to impaired stress recovery, sleep disturbances and metabolic dysfunction. The relationship runs both ways, and the source models the other direction explicitly: chronic sleep restriction itself produces physiologically relevant disruptions in the phase and amplitude of the cortisol rhythm (PMC8400645). Sleep loss and cortisol dysregulation drive each other. PMC2902103

It lowers Hair.

Cortisol from HPA-axis activation disrupts the hair-growth cycle and pushes follicles toward premature shedding (Thom 2016, J Drugs Dermatol, PMID 27538002) — the stress root of telogen effluvium and an androgenetic-alopecia aggravator. PMID 27538002

It lowers Supports BDNF signaling.

Smith 1995, J Neurosci 15:1768 — stress and glucocorticoids markedly reduce hippocampal BDNF mRNA. PMID 7891134

It lowers Mood.

Holsboer 2000, Neuropsychopharmacology 23:477 — impaired glucocorticoid-receptor feedback drives HPA hyperactivity and hypercortisolism in depression. DOI 10.1016/S0893-133X(00)00159-7. Convergent: HPA hyperactivity is described as a primary factor leading to depression under chronic stress, and cortisol is called one of the most significant biomarkers of depression. Mechanism: chronic HPA activation interacts with inflammatory pathways, generates oxidative stress, and produces structural and functional alteration of the hippocampus -- chronic cortisol exposure causes atrophy in hippocampus and amygdala. depression is explicitly multifactorial in these same reviews; HPA hyperactivity is one contributor. And the hippocampal change is reversible in many cases when stress exposure is reduced. doi 10.1016/S0893-133X(00

It raises Calm under stress.

Endocrine dysfunction of the hypothalamic-pituitary-adrenal axis is a core mechanism in anxiety: HPA activation drives glucocorticoid secretion and the negative-feedback loop that normally restrains it is impaired in anxiety disorders (review, DOI 10.3389/fnins.2024.1501134). Convergent: HPA axis dysfunction is associated with MDD, PTSD and anxiety, and cortisol is named one of the most significant biomarkers of anxiety disorders. 'biomarker of' is an association claim, not a demonstration of causation — the reviews do not establish that cortisol elevation causes the anxiety phenotype. doi 10.3389/fnins.2024.1501134

It raises Body clock.

Cortisol is a secondary entraining signal that coordinates local clocks throughout the body to the master clock: basal glucocorticoids peak at the habitual waking time, but only when the SCN is intact, and glucocorticoids induce Per1 through a glucocorticoid-response element in the Per1 promoter (PMC7744424). Note: this is a phase-setting relationship, not a more-is-better one — a cortisol rhythm entrains the clock; a flattened or chronically raised one does not. A direction caveat: this link is drawn from the HPA axis to the circadian clock, but the dominant direction in this literature is the reverse. HPA hormones exhibit ~24-hour rhythms that are primarily driven by the central circadian clock in the suprachiasmatic nucleus; cortisol peaks shortly after waking and declines through the day because the SCN sets it. The forward arrow is still defensible — HPA dysregulation flattens and phase-shifts the diurnal profile, and disrupted circadian rhythm is listed among the drivers of HPA dysfunction — so the true relationship is reciprocal. Only one direction is drawn here. The HPA axis is itself an AUTOREGULATORY negative feedback loop: cortisol negatively regulates CRH and ACTH. REFUTED ON A SECOND READING. This link was shown by linked steps until a source was opened that does not support it: “The hormones of the HPA axis exhibit regular approximately 24 h periodic rhythms that are primarily driven by the central circadian clock located in the hypothalamic suprachiasmatic nuclei (SCN).” — Modeling the Influence of Chronic Sleep Restriction on Cortisol Circadian Rhythms, with Implications for Metabolic Disorders. Journal name, volume and pages NOT READ (title READ via pubannotation.org full text). doi:10.3390/metabo11080483 | PMID 34436424 |. doi 10.3390/metabo11080483 · PMID 34436424 · PMC7744424

It lowers Mood (serotonin).

Raphe 5-HT neurons express glucocorticoid receptors, and corticosterone produces glucocorticoid-receptor-mediated inhibition of 5-HT1A autoreceptor functioning in the dorsal raphe (Laaris 1995). Chronic corticosterone additionally alters 5-HT7-receptor-mediated modulation of GABAergic transmission in the DRN, an effect ameliorated by the 5-HT7 antagonist SB 269970 — a pharmacological rescue. The sign is not simple and is recorded as such: blunting an inhibitory autoreceptor would DISINHIBIT firing, while the wider corticosteroid-serotonin literature treats the net effect on stress-related disorders as impairing. What is certain is that stress hormones rewrite the responsiveness of the serotonin source itself, not merely its downstream targets. doi 10.1007/s00213-018-5045-y

It raises Brain inflammation.

Glucocorticoids are the archetypal anti-inflammatory drug in the body. In the brain they do the opposite: a paper is titled glucocorticoids mediate stress-induced priming of microglial pro-inflammatory responses, and another finds glucocorticoids exacerbate lipopolysaccharide-induced signaling in the frontal cortex and hippocampus. Dose-dependent and molecularly specified: chronic corticosterone raised gene expression of NLRP3, Iba-1, MHCII and NF-kappa-B-I-alpha in a concentration-dependent manner; glucocorticoids induce NLRP3 at mRNA and protein level, priming inflammasome formation for a subsequent stimulus and potentiating the cytokine response. HPA hyperactivity drives overproduction of brain pro-inflammatory cytokines through microglial activation. The mechanism is disinhibition, not activation: stress DISINHIBITS microglia via down-regulation of CD200R — a brake is removed rather than an accelerator pressed. And the primed state outlasts the stressor by weeks: it is maintained as long as 24 days after the last stress, with primed microglia showing an exaggerated response to any subsequent immune challenge. That is why a past stressor changes how the next infection feels. doi 10.1212/NXI.0000000000200023

It raises Quiets overexcitation.

acute: glucocorticoids released during initial stress cause long-lasting potentiation of ampa and nmda receptor currents in pyramidal neurons, increasing surface expression of those receptors and improving working memory — the stress response sharpening the machinery it needs. Excess OR prolonged: the same combination exacerbates excitotoxic insults by increasing intracellular calcium, while high glucocorticoid levels deplete available energy and inhibit cellular growth. The authors conclude that over time it may become beneficial to limit the signals associated with acute stress in these regions — the same signal that helps briefly harms when held. doi 10.1186/s12974-021-02309-6

It lowers Curbs appetite.

The PNAS title states something stronger than an association: leptin's hunger-suppressing effects ARE mediated by the hypothalamic-pituitary-adrenocortical axis. An obligatory middle step: stimulation of hunger requires an intervening endocrine step, namely activation of the HPA axis. Increased corticosterone then activates AgRP neurons to fully increase hunger. Low leptin does not reach the hunger neurons directly — it goes via the stress axis. And the receptor is on the cell: AgRP neurons express glucocorticoid receptors, and corticosterone regulates the expression of AgRP and neuropeptide Y. The loop runs both ways: all psychological OR physical stressors increase plasma ghrelin, ghrelin strongly activates c-fos in CRF-producing neurons, and mice lacking the ghrelin receptor failed to show normal stress-induced alterations of mood, feeding and metabolism. Corticosterone activates AgRP to drive hunger, so the HPA axis reduces satiety. Drawn inhibitory. doi 10.1073/pnas.1901795116 · PMC3282735