What is the Circadian Rhythm?
The circadian rhythm refers to the body’s 24-hour clock that regulates the sleep/wake cycle in response to changes within the environment, primarily to light and darkness. These oscillations observed in the body are physical, mental, and behavioral changes that follow a daily cycle.
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From an evolutionary perspective, the circadian clock enables humans to adapt and anticipate changes in temperature, radiation, and the availability of food. Circadian rhythms are found in most living things, including animals, plants, and many tiny microbes.
Contemporary research into the effect of circadian rhythm on body systems suggests that it may play a role in weight homeostasis.
Circadian Rhythm and Weight Loss
Research published in Cell suggests that the time at which eating occurs during the day may impact success in losing weight. Specifically, the research found that eating meals late at night may desynchronize the internal body clock.
Researchers from the University of Manchester analyzed mice and cultured cells as part of the experiment. Research has established that insulin is released from the pancreas following the consumption of food to help stabilize blood glucose levels.
If food is ingested outside of typical mealtimes, then the subsequent release of insulin also occurs outside of a typical schedule.
As a result of this, the circadian rhythm can be disturbed, affecting both weight loss and weight gain. The mechanism in which this disturbance occurs is outlined below.
Cortisol, the stress hormone, typically peaks at 8 am, allowing individuals to wake from sleep, and falling to its lowest concentration at 3 am. This rise also occurs in line with exposure to sunlight. By noon, cortisol levels begin to fall inverse to serotonin and adrenaline, which elevates mood and energy.
The increase in energy levels, in particular, stimulates feelings of hunger and prompts the person to eat. Throughout the rest of the day, cortisol levels continue to decline, and serotonin is synthesized into melatonin, promoting feelings of sleepiness. Alongside this is a decrease in blood sugar levels, which drop to their lowest point at 3 am. This balance can be disturbed in those that snack late at night or eat meals outside typical times, affecting stress levels and digestion, the researchers argue.
The research found that insulin and the insulin-like growth factor – 1 (IGF-1) similarly synchronize with the body’s circadian rhythm. Upon the release of IGF-1, there is an increase in PERIOD clock proteins. During the experiment, the researchers altered the timings of insulin release and noted changes in circadian rhythms leading to altered behavior and gene expression in mice.
Researchers from the University of Manchester noted the importance of this research in relation to observed health trends. The findings propose that insulin can act as a timing signal for other cells within the body. Furthermore, the research adds to a body of evidence that circadian disruption is becoming more prevalent due to modern societal issues such as sleep deprivation and shiftwork.
Such disturbances can have a knock-on effect on the incidence and severity of diseases such as type 2 diabetes and cardiovascular disease.
Practical guidance based on the research includes the need to be mindful of when you eat to maintain healthy body clocks as we age. To help mitigate the adverse effects of shiftwork, paying attention to when you eat and light exposure may be beneficial.
Circadian Rhythm and Diabetes
Research has investigated the impact of circadian desynchrony in humans. It has found that those who engage in shift work pose an increased risk of developing type 2 diabetes, particularly women, and are only somewhat mediated by an increase in weight. In this instance, eating meals out of sync from typical patterns mainly affect glucose levels inducing diabetes, rather than causing issues with weight management.
Men who had previously shift worked were still more likely to be diagnosed with the metabolic disorder compared to men who had never worked a job with a shift work pattern. This suggests that the effects of disrupted circadian rhythm may not be entirely reversible.
Circadian Rhythm and Cardiovascular Disease
The impact of shift work and the increased risk of cardiovascular disease has been studied. Research has found that shift workers with circadian misalignment were observed to have an increase in cardiovascular and blood pressure markers such as TNF-α, IL-6, and C-reactive protein.
Video - How eating feeds into the body clock
- Thosar, S. T. et al. (2018). Role of circadian system in cardiovascular disease. The Journal of Clinical Investigation. Doi: 10.1172/JCI80590
- Hutchinson, A. T. et al. (2017). Matching Meals to Body Clock – Impacts on Weight and Glucose Metabolism. Nutrients. Doi: 10.3390/nu9030222
- Reddy, S., & Sharma, S. (2018). Physiology, Circadian Rhythm. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK519507/
- Wilcox, G. (2005). Insulin and Insulin Resistance. The Clinical Biochemist Reviews. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1204764/
- Insulin/IGF-1 Drives PERIOD Synthesis to Entrain Circadian Rhythms with Feeding Time Crosby, Priya et al. Cell, Volume 177, Issue 4, 896 - 909.e20, https://www.cell.com/cell/fulltext/S0092-8674(19)30166-7
- Mandal, Ananya. 2019. Circadian rhythm plays a part in weight loss. News-Medical, www.news-medical.net/.../...an-rhythm-plays-a-part-in-weight-loss.aspx.