The medical term circadian rhythm
was created to describe the oscillations in the human body functions observed during 24 hours. The function of the circadian rhythm
is to act as a regulator of cells and coordinate the internal physiological and behavioral processes in humans. The circadian rhythm
plays a very important role in human health
While it is argued that the autonomous rhythms must align with the earth’s daily rotation to regulate sleep/wake cycles in humans in line with light changes within the environment. Research suggests that the circadian rhythm
is central to human evolution, allowing us to adapt and anticipate environmental changes such as temperature, radiation, and the availability of food.
Typically, dysfunction in circadian rhythms
can cause a range of issues such as disturbances in sleep/wake cycles and mood disorders. The function of the circadian rhythm
has been well researched, with contemporary work analyzing the relationship between the immune system and the circadian rhythm
Medical researchers from Switzerland have recently published a review investigating the link between the circadian rhythm
and the development of illnesses such as allergies and cardiovascular difficulties such as heart attacks.
The study findings, containing mainly mice studies, found there to be a relationship between the immune system and the circadian rhythm
. Specifically, the studies found that adaptive immune responses, whereby specialized immune cells are synthesized to fight invading pathogens are regulated by the circadian clock.
The researchers told Thailand Medical
News that from the research, is suggested that the body’s response to cues, for example, hormones and light, affects sleep patterns and metabolic processes, amongst other biological activities. The researchers found the circadian rhythm
to be implicated in heart attacks
, atherosclerotic plaques, infections and toxins, and allergies.
The medical researchers found that heart attacks occur more commonly and severely in the morning, in comparison to at night. In animal studies, mice were found to have higher levels of blood monocytes during the daytime. Experiments showed that mice had more monocytes and larger infarctions during the night than during the day.
Typically, the immune system produces cells that help to protect against plaques that build up in the arteries. Research has found that the extent to which these cells are effective in upholding this aim is dependent on the circadian rhythms
of CCR2, a chemokine protein. CCR2 is typically involved in the function of the immune system and inflammatory processes.
Animal model studies have found the protein to follow a daily rhythm. Specifically, it is suggested to be highest in the morning. Based on its implications on immune cells, it has been found to monitor white blood cells involved in atherosclerosis.
Animal models appear t
o be differently able to respond to parasite infections depending on the time of day they are exposed. Mice responded to parasite infections with Trichuris muris more quickly when exposed in the morning compared to the evening.
Studies have found that responses to toxins may be greater in the afternoon. Mice infected with a bacterial toxin that triggers pulmonary inflammation respond differently depending on the time of exposure. If exposed in the afternoon, a larger number of monocytes were drawn into the peritoneal cavity, liver, and spleen resulting in a greater ability to fight the bacteria, compared to other periods of the day.
The study showed that allergy symptoms tend to be worst between midnight and early morning. Mast cell and eosinophil expression appear to vary based on circadian rhythms in mice.
The medical researchers have found that the severity of sepsis infections may be worse during the evening compared to the morning. Cell adhesion expression and neutrophil infiltration response to lipopolysaccharide septic shock were found to be higher in the evening. This worsening parallels with an increased risk of mortality during that time.
This is just example highlighting the relationship between the immune system and circadian rhythm
. There are other similar ones found between other bodily systems. For example, within the cardiovascular system, research has reported that in the morning compared to the night time individuals have: a higher heart rate, higher blood pressure, vasoconstriction, and a reduction in parasympathetic tone and thrombolytic activity.
For more details about the circadian rhythm
and correlations with other bodily systems, kindly refer to the studies listed below.
Reddy, S., & Sharma, S. (2018). Physiology, Circadian Rhythm. Stat Pearls. https://www.ncbi.nlm.nih.gov/books/NBK519507/
Scheiermann, C., Kunisaki, Y., & Frenette, P. S. (2014). Circadian control of the immune system. Nature Reviews Immunology. DOI: 10.1038/nri3386
Farhud, D., & Aryan, Z. (2018). Circadian Rhythm, Lifestyle and Health: A Narrative Review. Iranian Journal of Public Health. ncbi.nlm.nih.gov/pmc/articles/PMC6123576/
Thosar, S. S., Butler, M. P., & Shea, S. A. (2018). Role of the circadian system in cardiovascular disease.
Pick, R., He, W., Chen, C. S., & Scheiermann, C. (2019). Time-of-Day-Dependent Trafficking and Function of Leukocyte subsets. Trends in Immunology. DOI: https://doi.org/10.1016/j.it.2019.03.010