Key Benefits

• Check your body’s stress hormone balance and daily rhythm for adrenal health.
• Spot adrenal underactivity causing fatigue, weight loss, low blood pressure, salt craving.
• Flag cortisol excess driving weight gain, high blood pressure, diabetes risk, muscle weakness.
• Clarify stress-related symptoms like poor sleep, anxiety, brain fog, and mood shifts.
• Guide evaluation of infertility or irregular periods when stress hormones disrupt ovulation.
• Support pregnancy care when adrenal disorders affect blood pressure, glucose control, and fetal growth.
• Track recovery after steroid therapy by monitoring stress-system suppression and relapse risk.
• Best interpreted with 8 a.m. sample, ACTH, and your symptoms.

What is Cortisol?

Cortisol is the body’s principal stress hormone (a glucocorticoid steroid) made in the outer layer of the adrenal glands (adrenal cortex, zona fasciculata) from cholesterol. Its release is governed by the brain’s stress circuit (the hypothalamic–pituitary–adrenal, HPA, axis): the pituitary sends adrenocorticotropic hormone (ACTH) to trigger cortisol production. Cortisol follows a daily rhythm (circadian pattern), rising in the early morning to help you wake and dipping to its lowest around midnight.

Cortisol readies the body to meet demand. It frees glucose for fuel (stimulates gluconeogenesis), shifts the body toward using fat and protein, and supports blood pressure and blood vessel responsiveness (vascular tone). It also tempers immune activity and inflammation, shaping how you recover from illness or injury. Inside cells, cortisol binds the glucocorticoid receptor (NR3C1) to adjust gene activity across many tissues, influencing energy, mood, alertness, and resilience to stress. In this way, cortisol reflects the tone of the HPA axis and coordinates metabolism, immunity, and the sleep–wake cycle so the body can adapt to both daily rhythms and unexpected challenges.

Why is Cortisol important?

Cortisol is the body’s daytime accelerator. Released by the adrenal glands under direction of the brain’s stress system (the HPA axis), it mobilizes fuel, keeps blood pressure responsive, tempers inflammation, sharpens attention, and helps set the sleep–wake rhythm. It peaks within 30–60 minutes after waking, then steadily declines to very low levels near midnight. Most labs define a broad morning reference band; in healthy adults, values sit near the middle of that morning range, with clearly low late‑night levels and a steep daytime slope.

When cortisol is lower than expected for the time of day—or the curve is flat—energy delivery and vascular tone sag. People often feel profound fatigue, dizziness on standing, brain fog, nausea, salt craving, and low mood; blood pressure, sodium, and glucose can run low. Primary adrenal failure can add skin darkening, while pituitary causes lack this. Children may have poor growth or recurrent hypoglycemia. Women can notice cycle irregularity. After pregnancy, values gradually reset toward nonpregnant ranges.

When cortisol runs high—or stays elevated at night—the body shifts toward storage and wear‑and‑tear. Central weight gain, high blood pressure, high glucose, thin skin with easy bruising, bone loss, infections, anxiety or irritability, and poor sleep can emerge. Women may have irregular periods or hirsutism; men may note reduced libido. In children, slowed linear growth despite weight gain is a red flag. Pregnancy raises total cortisol physiologically, so ranges shift upward.

Big picture: Cortisol connects brain, adrenals, metabolism, immunity, bone, and cardiovascular systems. Persistent dysregulation—too much, too little, or a blunted rhythm—tracks with diabetes risk, osteoporosis, depression, and heart disease, underscoring why timing, pattern, and context matter.

What Insights Will I Get?

Cortisol measures the output of your stress-response system (the hypothalamic–pituitary–adrenal axis). It mobilizes fuel, stabilizes blood pressure, shapes circadian alertness, and modulates memory, mood, immunity, and reproductive signaling. Most circulating cortisol is protein-bound; the free fraction is biologically active. Levels normally peak in the early morning and fall across the day.

Low values usually reflect underproduction of adrenal hormone (adrenal insufficiency/Addison’s), reduced pituitary drive (low ACTH), or suppression after glucocorticoid exposure. Systems-level effects include low energy, low blood pressure, low glucose, poor stress tolerance, and higher inflammation. Menstrual irregularity and low libido can occur when adrenal androgens are reduced. Children have lower absolute levels; pregnancy rarely shows low total cortisol.

Being in range suggests an intact stress axis with appropriate fuel delivery, blood pressure stability, balanced immune tone, and steady cognition and mood. Optimal positioning depends on the clock: relatively higher in the morning and lower later. A mid-to-upper value in the morning and clearly lower later in the day generally indicates a healthy circadian rhythm.

High values usually reflect heightened stress signaling (pain, illness, sleep loss), major depression, or endogenous overproduction (Cushing physiology from pituitary/adrenal disease). Systems-level effects include higher glucose and insulin resistance, elevated blood pressure, central fat gain, bone and muscle loss, immune suppression, and sleep and mood disturbance. Pregnancy and oral estrogens raise total cortisol by increasing binding proteins.

Notes: Interpret by time of day, sleep/shift pattern, posture, and acute illness. Total versus free cortisol differs when binding proteins change (pregnancy, estrogen therapy, liver disease). Assays vary (immunoassay vs LC–MS). Age flattens the daily curve; pediatric ranges differ. Recent steroids suppress values.