Circadian Rhythms and Your Immune System- Part 1

Circadian Rhythms and Your Immune System

Why is there an increased risk of colon cancer the farther we live from the equator? (Bostick 2015, Dimitrov and White 2016) What is the connection between chronic insomnia and joint disease? Without ignoring environment (stress, diet, air quality) to account for chronic degenerative diseases, we often overlook the body’s daily rhythm of “break-clean-repair,” and how we lose the “repair” part of the rhythm when we lose sleep, when we are too stressed, or when we do not take care of our health.

Part 1: Cortisol, the morning hormone.

The adrenal hormone cortisol is often associated with stress. The media discusses cortisol in the context of “adrenal fatigue” and “adrenal stress.” Both are reflective of the body’s capacity to pump out cortisol in response to stress. While this is all true to some degree – especially the part about cortisol production during stress – there are other factors that are more powerful than contemplating cortisol and the adrenals as a punching bag during stressful events. And that is: the circadian rhythm of cortisol production in the morning – the primary focus of which is to dial down the immune system and to scavenge the tissues to feed the brain with glucose.

Most of the healing is done at night while we are sleeping. And because we need the immune system working optimally, the body can’t afford to have high cortisol levels at night. Otherwise, it would shut down the parts of the immune system that migrate into torn and injured tissues and deposit goodies that repair the damage. High cortisol at night would destroy the repair process.

However, cortisol does come into play at night, if for no other reason than to prepare for the morning cortisol surge. Here’s an idea how that might happen. Because we don’t eat at night while sleeping, a healthy body has built-in ways to deal with nighttime drops in blood sugar. There are two ways to do it without eating.

Blood sugar typically reaches a low mark around 2 a.m. When this drop happens, the body can release catecholamines (like adrenaline), and that will get the liver to release sugar into the blood system. Problem solved? Not really. Adrenaline is the fight/flight hormone and it will wake you up every time your blood sugar drops. If anyone complains that they wake up in the middle of the night starving… If anyone needs to have a bowl of cereal at 2 a.m. before going back to sleep… catecholamines are at work. And this is not good.

The other way to boost nighttime blood sugar is for the body to release a bit of cortisol – just enough to compel the release of sugar from the muscles and tissues. And this doesn’t wake you up. For a healthy metabolism, this cortisol release happens about every two hours, and each time, cortisol levels in the blood add to the leftovers of the last round of cortisol release. By around 5 or 6 a.m., when the sum of the night’s accumulated cortisol reaches a critical mass, the brain (paraventricular nuclei, specifically) triggers a stress response and your brain gets a flood of sugar: wake-up time (Fig.1).

6 to 11 a.m. – The Immune System’s “Off” Time

For most of us, the morning hours are a time to do work. Looking further back in our history, farming and agricultural communities would wake up even earlier to make the best use of daylight. The early morning is high time for cerebral, planning activities, and slowly merges the physiology into the heavier work part of the day.

Why cerebral in the morning? In the early morning, the body naturally produces its highest yield of cortisol. This hormone serves two important purposes:

  1. Cortisol suppresses immune function. Immunosuppression minimizes the irritation of inflammation, and subsides other aspects of the immune system that might intensify fever. It frees up the metabolism to transition energy to other things – to do work.
  2. Cortisol shifts glycogen (stored sugar) energy from tissue storage to the blood system. This makes blood sugar more available to non-insulin reliant tissues like your brain, eyes, and remaining nervous system. Its activity compels a constant, stable flow of energy to the brain.

Fig 1 Cortisol levels surge early in the morning after several small bursts of cortisol during the night. Steep rise in the morning suppresses inflammation, reduce environmental sensitivity, and stabilize blood sugar while we are at work in the morning.

Cortisol also degrades connective tissue, as evidenced by damage to tissues treated directly with steroid (glucocorticoid) medicines.(Asboe-Hansen 1976, Oikarinen, Uitto et al. 1986) While these observations are made primarily as a course of treatment with medication, we assume this remains true, albeit to a lesser degree, with physiological levels of cortisol production.(Pratt 1978)

The morning is dominated by cortisol. It acts to suppress inflammation, the immune response, and it suppresses healing. Cortisol also stabilizes blood sugar, which fuels the brain and the nervous system. This is a circadian pattern that encourages productivity but also, if uncapped, will lead to degradation of bone, joint, and muscle. The immune system’s “off” time cannot persist, otherwise healing and regeneration of these tissues would not occur.

In our next segment, we will continue our discussion of the circadian rhythm and how this influences immune function. We will take a look at the afternoon hours, and a different set of hormones that help us get through the work day.


Asboe-Hansen, G. (1976). “Influence of corticosteroids on connective tissue.” Dermatologica 152 Suppl 1: 127-132.

Bostick, R. M. (2015). “Effects of supplemental vitamin D and calcium on normal colon tissue and circulating biomarkers of risk for colorectal neoplasms.” J Steroid Biochem Mol Biol 148: 86-95.

Dimitrov, V. and J. H. White (2016). “Species-specific regulation of innate immunity by vitamin D signaling.” J Steroid Biochem Mol Biol 164: 246-253.

Oikarinen, A. I., J. Uitto and J. Oikarinen (1986). “Glucocorticoid action on connective tissue: from molecular mechanisms to clinical practice.” Med Biol 64(5): 221-230.

Pratt, W. B. (1978). “The mechanism of glucocorticoid effects in fibroblasts.” J Invest Dermatol 71(1): 24-35.

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