Cortisol is produced by the adrenal glands in response to stimulation of the pituitary gland by the adrenal corticotropic hormone (ACTH), an essential hormone in cases of stress (illness, surgery, hypoglycemia, etc.). Cortisol also has a major anti-inflammatory effect and weakens the immune system. It inhibits sex hormone production and bone formation, promotes the formation of blood clots and leads to high blood pressure.
Cortisol levels vary with the time of day: high in the early morning to help the body cope with the stress of a new day and low in the evening before the period of calm associated with bedtime.
Cortisol levels are interpreted by taking into account the time of day (morning or afternoon), urinary cortisol and ACTH levels, and the use of medications containing corticosteroids which may interfere with the assay.
Cortisol levels can be measured in the blood, urine or saliva.
Above-normal urinary cortisol levels usually indicate hyperfunction of the adrenal glands (Cushing’s syndrome), possibly due to hyperstimulation by ACTH (pituitary gland disorder) or uncontrolled adrenal gland function (hyperplasia or tumour). In the latter case, higher cortisol levels are accompanied by lower ACTH levels.
Reduced cortisol levels (Addison’s disease) indicate either hypostimulation of the adrenals by ACTH (pituitary disorder) or a problem with the adrenal glands themselves (autoimmune disease, infection, cancer or other causes of gland destruction).
When cortisol levels are insufficient to meet the body’s needs, the body secretes increased amounts of ACTH, which will stimulate the adrenal glands to produce cortisol.
People with abnormally low cortisol levels can be at risk if their body is under severe stress (severe hypoglycemia or surgery).