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Cortisol: The "Stress Hormone"
The hormone cortisol, which is released in the body during stressed or agitated states, has gained widespread attention as the so-called "stress hormone." But this hormone is more than a simple marker of stress levels - it is necessary for the functioning of almost every part of the body. Excesses or deficiencies of this crucial hormone also lead to various physical symptoms and disease states.
Background
Cortisol is a steroid hormone made in the adrenal glands, which are small glands adjacent to the kidneys. Among its important functions in the body include roles in the regulation of blood pressure and cardiovascular function as well as regulation of the body's use of proteins, carbohydrates, and fats. Cortisol secretion increases in response to any stress in the body, whether physical (such as illness, trauma, surgery, or temperature extremes) or psychological. When cortisol is secreted, it causes a breakdown of muscle protein, leading to release of amino acids (the "building blocks" of protein) into the bloodstream. These amino acids are then used by the liver to synthesize glucose for energy, in a process called gluconeogenesis. This process raises the blood sugar level so the brain will have more glucose for energy. At the same time the other tissues of the body decrease their use of glucose as fuel. Cortisol also leads to the release of so-called fatty acids, an energy source from fat cells, for use by the muscles. Taken together, these energy-directing processes prepare the individual to deal with stressors and insure that the brain receives adequate energy sources.
The body possesses an elaborate feedback system for controlling cortisol secretion and regulating the amount of cortisol in the bloodstream. The pituitary gland, a small gland at the base of the brain, makes and secretes a hormone known as adrenocorticotrophin, or ACTH. Secretion of ACTH signals the adrenal glands to increase cortisol production and secretion. The pituitary, in turn, receives signals from the hypothalamus of the brain in the form of the hormone CRH, or corticotropin-releasing hormone, which signals the pituitary to release ACTH. Almost immediately after a stressful event, the levels of the regulatory hormones ACTH and CRH increase, causing an immediate rise in cortisol levels. When cortisol is present in adequate (or excess) amounts, a negative feedback system operates on the pituitary gland and hypothalamus which alerts these areas to reduce the output of ACTH and CRH, respectively, in order to reduce cortisol secretion when adequate levels are present.
Measurement of Cortisol levels
The body's level of cortisol in the bloodstream displays what is known as a diurnal variation - that is, normal concentrations of cortisol vary throughout a 24-hour period. Cortisol levels in normal individuals are highest in the early morning at around 6-8 am and are lowest around midnight. Normal levels of cortisol in the bloodstream range from 6-23 mcg/dl (micrograms per deciliter). In addition to early morning, cortisol levels may be somewhat higher after meals. While the most common test is measurement of the cortisol level in the blood, some doctors measure cortisol through a saliva sample, as salivary cortisol levels have been shown to be an index of blood cortisol levels. Sometimes by-products of cortisol metabolism are also measured, such as 17-hydroxycorticosteroids, which are inactive products of cortisol breakdown in the liver. In some cases measurement of urinary cortisol levels is of value. For this test, urine is collected over a 24-hour period and analyzed. Normal 24-hour urinary cortisol levels range from 10-100 micrograms/ 24 hours.
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