Many of the hormones in the body maintain a roughly 24-hour rhythm, controlled by the suprachiasmatic nucleus (SCN) - also known as the body clock - in the hypothalamus. The HPA axis is one of the most important circadian rhythms in the body, as it has such a great influence over health, vitality and the immune system.
Figure: Typical variation in cortisol levels throughout the day
Abnormal hormone rhythms have been implicated in illnesses such as chronic fatigue syndrome (CFS), irritable bowel syndrome (IBS), seasonal affective disorder (SAD) and insomnia. Research shows that CFS patients tend to have a less pronounced circadian rhythm of HPA axis activation, and that the patients who recover most tend to have the greatest increase in circadian hormone variation.
Having a circadian rhythm rather than a constant level of certain hormones, such as cortisol and melatonin, is important to many systems in the body, and the abolition of the normal rhythm is likely to cause many of the symptoms associated with illnesses such as CFS.
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