Life as we know it is built around the sun’s 24-hour cycle. Your independent “body clock” – your circadian rhythm - also works on a 24-hour cycle, and is synchronized with the natural time cues of each day, like sunlight and darkness. The circadian rhythm not only regulates sleeping and waking states, but every biological system in the body. For this reason, circadian rhythms have a massive impact on health, disease and performance.
With modern, 24/7 lifestyles being heavily reliant on technology, our circadian rhythms are more misaligned with the solar cycle than ever, be it through travel jet lag, social jet lag (yes, that’s a real term) or night shift work. The resulting mistimed exposure to light and dark exposure can disrupt our internal processes, elevating the risk of illness or disease affecting cardiovascular, metabolic and gastrointestinal systems, mental health, contributing to the development of some forms of cancer and all-cause mortality.
As with anything wellness-related, a deepened understanding can help us to be proactive to reclaim and enhance health, recovery and performance.
How the Circadian Rhythm Works
Our circadian rhythm is controlled by a “central clock” in the brain, which synchronizes a number of “peripheral clocks” in different parts of the body, to regulate internal processes and maintain a state of homeostasis with external time cues. These processes include heart rate and blood pressure, immunity, metabolism, body temperature, sleep, hormone function and even mood. The main external time cues are light and darkness, ambient temperature, physical activity and feeding times.
A group of researchers discovered that the daily co-ordination of our physiology with the environment is controlled by “clock genes” in our DNA. This finding led to a Nobel prize for medicine, due to the impact this has on health. Interestingly, whether you are an “early bird” or “night owl” is also determined by this same set of genes.
Technology and “Lightmares”
We would not be the civilized species we are today without the technology we have at our hands. Some would argue that we would not be able to function or compete at all in this globalized world. However, with people now being more active during the body's “biological night-time” when the internal clock is signalling sleep, less time is available for vital regeneration processes that only happen during sleep. Whether you are an “early bird” or “night owl”, all humans have a biological need for sleep. On average, we spend one-third of our lives asleep or trying to sleep.
Health Implications of Circadian Misalignment
Circadian disruptions may be temporary, as with travel between time zones or a change to daylight savings time, or more permanent as with ongoing shift work. Night shift work, in particular, may cause chronic circadian misalignment and have a negative influence on health. Social jetlag is another disruption, which a large number of people experience when their social schedules interfere with their biologically preferred sleeping and waking times.
Poor sleep quality, short sleep duration and mistimed sleep are associated with an increased risk of conditions such as cardiovascular disease, insulin resistance, type 2 diabetes, obesity, metabolic syndrome, gastrointestinal disorders, mental and psychiatric disorders, some forms of cancer and all-cause mortality.
So as much as sleep can be a thoughtless state we encounter, it’s worth having a consistent routine to optimize the timing, duration and quality of your sleep. In my previous article, Staying Grounded During the COVID-19 Pandemic, I outline some basic sleep hygiene strategies. The National Sleep Foundation (a great resource for all things sleep) outlines the following age-related recommendations:
New born (0-3 months): 14-17 hours each day
Infant (4-11 months): 12-15 hours
Toddler (1-2 years): 11-14 hours
Pre-schooler (3-5): 10-13 hours
School child (6-13): 9-11 hours
Teenager (14-17): 8-10 hours
Younger adult (18-25): 7-9 hours
Adult (26-64): 7-9 hours
Older adult (65+): 7-8 hours
Exercise and the Circadian Rhythm
Similar to light, exercise helps to keep the circadian rhythm synchronized. Engaging the skeletal muscles in exercise positively influences and regulates blood pressure, heart rate, and the key sleep hormone melatonin. The exact duration, intensity and timing of exercise for these enhancing effects is not known, and this might vary depending on whether you are an “early bird” or “night owl.” However, sleep quality and duration and is higher in individuals who regularly engage in physical activity than those who do not.
Meal-Timing and the Circadian Rhythm
What time we exercise, eat, or sleep can fluctuate daily for multiple reasons like work deadlines, travel, stress, social obligations or using devices late into the night, contributing to a lack of routine. There is growing evidence to suggest that synchronizing mealtimes with our circadian rhythms leads to significantly more weight loss and reduced insulin resistance than if you ate the same food without a schedule, no matter how healthy it is. In the age-old way that humans ate, there were periods of food scarcity which naturally led to a state of intermittent fasting. Today, food scarcity is not a widespread reality and behaviour around food is mainly influenced by lifestyle, industry and culture.
Conclusion
Circadian rhythms with the help of environmental time cues, align our physiology to enhance physical function and well-being. Being in tune with our lifestyle habits is vital to unlocking the benefits of this optimization, to support all facets of life as we know it.
Terminology
Circadian rhythm – Internally-regulated recurring patterns of about 24 hours with well-established roles in physiology and behaviour.
Entrainment – Synchronization of the internal circadian rhythm with the external solar cycle.
Zeitgebers – Environmental cues that entrain the body's circadian rhythm to the 24-hour solar cycle.
Homeostasis – The tendency to maintain a stable, relatively constant internal environment of the body.
Hypothalamus – A small region at the base of the brain that houses the central clock and maintains homeostasis of the body.
Chronotype – Genetic expression of preferred sleep and wake times, and also peak performance.
Early bird – The chronotype whose daily peak performance occurs early during the day.
Night owl – The chronotype whose daily peak performance occurs later in the day.
Melatonin – Hormone that stimulates the body to feel tired and sleep. Naturally produced after dark exposure at night
Jet lag – Disruption in circadian rhythms caused by travel across time zones.
Social jet lag - The daily and ongoing discrepancy between social time (when an individual's sleep and wake time is dictated by social or work obligations) and internal biological time.
All-cause mortality - The death rate from all causes of death for a population in a given time period.
Insulin resistance - The diminished ability of cells to respond to the action of insulin in transporting glucose from the bloodstream into muscle and other tissues, resulting in an increase in blood sugar levels.
Resource
Timeshifter app – Helps adjust your circadian rhythm to changes in time zone during and after travel
This article was featured in Harare Magazine
Works Cited
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National Sleep Foundation.org: https://www.sleepfoundation.org/articles/how-much-sleep-do-we-really-need
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Hower, !., Harper, S., & Buford, T. (2018). Circadian Rhythms, Exercise, and Cardiovascular Health. Journal of Circadian Rhythms, 1-8.
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McGroarty, B. (2020). 2020 Wellness Trends. Global Wellness Summit.