Circadian Rhythms and our Immune Systems

Circadian rhythms were first discovered in plants with their relationship with the light cycle of the sun.  The scientific community then started to realize that circadian rhythms are present in every life form we have looked at, and furthermore in every cell in the human body.  The more we learn about circadian rhythms, the more we learn that it plays a role in most functions in our bodies in one way or another.  

Before electricity being easily accessible, there were not a lot of opportunities for circadian rhythms to be disrupted.  Since electricity has allowed humans to continue to function and work in the dark hours of the day, we have been able to disrupt these circadian cycles that have been formed and evolved over thousands of years.  These disruptions can be from various things like working overnight shifts, frequent jet lag, or even eating at irregular times.  

There is now a lot of research that looks at the health consequences of disrupted circadian rhythms.  What we have found is alarming.  The effects range from higher risk of heart disease and diabetes to higher risk of cancer and obesity.  It seems to be that nearly every bodily function and system has evolved to work in a rhythm, and when that rhythm is thrown off, there are medical issues.  It has even been found that the immune system is dependent on our circadian rhythm.

Our bodies function in a state of homeostasis and balance.  The body uses hormones to communicate from organ to organ and system to system.  When that balance and communication is lost, systems become dysfunctional, and the continued dysfunction leads to bigger health problems.  The immune system is part of our homeostasis machinery and is dependent on circadian rhythms.  Like most of the homeostasis network, the immune system functions with hormones, specifically the endocrine system.  The endocrine system monitors and regulates the immune system, so if it malfunctions, the immune system suffers and can result in autoimmunity, septic shock, or chronic infection.  It is believed that our immune system evolved this way to maximally function during the most likely times of pathogen exposure and to utilize rest as a time for tissue repair. 

References

O. A. Habbal & A. A. Al-Jabri (2009) Circadian Rhythm and the Immune Response: A Review, International Reviews of Immunology, 28:1-2, 93-108, DOI: 10.1080/08830180802645050

Turek, F., & Summa, K. (n.d.). Circadian Desynchrony and Health. In Atlas of Clinical Sleep Medicine (pp. 168–174).

Waggoner, S. (2020). Circadian Rhythms in Immunity. Basic and Applied Science, 20.