Circadian Rhythms and the Human Immune System

             Some behaviors of many organisms are under the control of 24-hour cycles we call circadian rhythms. These rhythms regulate many biological and physiological behaviors such as sleeping, eating, and hormone release. These rhythms are mostly controlled by the light and darkness of an organism’s environment. By studying circadian rhythms, one can better understand the conditions that lead to a better quality of life, such as a routine-based sleeping schedule.

            Other organisms are often utilized for the study of circadian rhythms, as they also display these 24-hour cycles. In the article, “Central and Peripheral Clock Control of Circadian Feeding Rhythms” Fulgham et al. investigate the effect that ventrolateral clock neurons of the central brain and the fat body, a peripheral metabolic tissue, have on the feeding behavior of drosophila melanogaster, the fruit fly. By manipulating clock neurons in the central brain and the fat body, they found that central brain clocks serve as a pacemaker for feeding rhythms, but the peripheral clock does not. The peripheral clock was found to make subtle changes to regulate feeding behavior, shown when the disruption of peripheral clocks led to dampened feeding rhythms. The study demonstrates how circadian rhythms control biological functions, in this case feeding rhythms. Furthermore, it also illustrates how complex the neural pathways coding these feeding rhythms can be.

            In a different study also focused on circadian rhythms, researchers investigated how sleep and the immune system play in role within our 24-hour cycles. In the article, “Effects of sleep and circadian rhythm on the human immune system,” Lange et. al. writes how sleep and the circadian system work bidirectionally at the suprachiasmatic nuclei and with clock genes to organize immune functions through neuroendocrine and sympathetic effector mechanisms. They found that cortisol levels show a circadian low-point during night, and are suppressed by sleep. However, growth hormone and prolactin show a peak during night, and are enhanced by sleep. This shows that the circadian system and sleep both evoke a unique endocrine group that is very effective in inducing changes in leukocytes and a shift toward proinflammatory type 1-cytokines during periods of sleep. If this 24-hr cycle of sleep and wakefulness is disrupted, as seen in shift-workers, it compromises one’s wellbeing and health. They state that epidemiological data suggests that shift workers are at an advanced risk for cancer and rheumatoid arthritis due to these disrupted sleeping and waking rhythms.

            Overall, the study of circadian rhythms is of great and useful importance. As circadian rhythms affect our physiology and behavior, our greater understanding of it has the potential to improve the health and quality of life of those who need it, such as shift workers with disrupted circadian rhythms.

Sources:

 Fulgham, C. V., Dreyer, A. P., Nasseri, A., Miller, A. N., Love, J., Martin, M. M., Jabr, D. A., Saurabh, S., & Cavanaugh, D. J. (2021). Central and Peripheral Clock Control of Circadian Feeding Rhythms. Journal of Biological Rhythms, 36(6), 548–566. https://doi.org/10.1177/07487304211045835

Lange, T., Dimitrov, S., & Born, J. (2010). Effects of sleep and circadian rhythm on the human immune system. Annals of the New York Academy of Sciences, 1193(1), 48–59. https://doi.org/10.1111/j.1749-6632.2009.05300.x