BIO RYTHMS

Every day I discuss adrenal health with practitioners and the importance of assessing a patient’s circadian rhythm. But last week someone asked me “what is the circadian rhythm?” Although I was able to explain the concept in simple terms, I started thinking – this is anything but simple…what is a circadian rhythm really?

The term circadian is derived from the Latin words “circa” meaning around and “diem” meaning day, translated 24 hours. Wikipedia defines the circadian rhythm as a 24-hour cycle in the biochemical, physiological or behavioural processes of living entities. Science has set specific criteria to identify a true endogenous circadian pattern:

1) The rhythm persists in constant conditions in a 24 hr period.
2) The rhythm persists over a range of temperatures.
3) The rhythms can be reset by exposure to an external stimulus.

My tendency was to think of the body’s circadian rhythm as primarily pertaining to the adrenal glands and cortisol synthesis. However, this does not seem to be the case. There are many autonomic, endogenous processes, besides cortisol secretion, that have a 24 hour circadian rhythm, including control of body temperature, cardiovascular function (heart rate and blood pressure), melatonin secretion, metabolism and sleep. Many of these are interrelated, affecting each other. For example, melatonin levels usually run opposite those of cortisol, but both have a 24 hour cycle. High night time cortisol levels may delay the normal rise of melatonin affecting sleep patterns.

Circadian patterns in mammals are controlled by the suprachiasmatic nucleus (SCN), a small group of cells located in the anterior hypothalamus of the brain acting as a pacemaker. Neuronal pathways into the SCN from other parts of the brain, along with fibers from the SCN to target tissues, result in a stable system of circadian rhythms. However, alterations to this system can occur. The environmental factor of the light/dark cycle of day and night is important for keeping circadian rhythms synchronized. Visual signals of light from the retina are sent to the SCN through the retinohypothalamic tract (RHT). These signals are then used to “set” our internal clocks and endogenous circadian rhythms. In contrast, research has shown that blindness or even constant darkness can alter the “settings” and lead to variations of the diurnal rhythm and secretion of several hormones, including melatonin, cortisol, growth hormone and gonadotropin hormones (FSH & LH). http://www.ncbi.nlm.nih.gov/sites/entrez

Although my search started with what I thought was a straightforward question about adrenal health and cortisol, it unexpectedly uncovered a larger field of study specializing in biological and circadian rhythms. I should have realized that anything to do with hormones is complicated, one piece of a puzzle leading to another. Yet, the normal, physiological pattern of cortisol, morning elevation and evening decline, is important for a healthy life, if only as a single part of the whole.

Sherry LaBeck, ND