Pearl Lee, PharmD, IFMCP

Your Circadian Rhythm: What is it and Why Does it Matter?

The circadian rhythm is your body’s internal clock responsible for regulating your sleep/wake cycles, body temperature and productivity through hormones and neurotransmitters. It determines whether you’re a “morning” or a “night” person. The two primary hormones in effect are cortisol, which gives us energy (high in the morning) and melatonin (high at night). Cortisol fuels our motivation, gives us drive and helps us focus. Meanwhile, melatonin makes us feel sleepy and helps us fall and stay asleep.

How does it work?

The ‘central’ clock, located in an area of the brain called the suprachiasmatic nuclei, is highly sensitive to light. When the sun rises in the morning, light promotes melatonin to be suppressed and cortisol to rise. This ‘central’ clock also manages the ‘peripheral’ clocks, which are also affected by other environmental inputs. For example, cells in your liver and intestines are affected by the consumption of food.

Why should I pay attention to it?

A synchronized circadian rhythm decreases stress in your body and provides numerous benefits, including:

  • Feeling well rested
  • Reduced hunger and cravings for sugary and/or highly palatable snacks (ie – cookies, chips)
  • Increase in productivity
  • Weight management
  • Stronger immunity
  • Improved mental health
  • Enhanced long term health including a decreased risk for metabolic syndrome (ie – cardiovascular disease, diabetes, weight gain) and cancer
  • Improved gut microbiome 

What is Chronotype? How do I use it to my advantage?

Your chronotype dictates whether you’re a “morning” or “night” person. Do you sleep in or wake up early? Do you wake up easily, or hit the alarm multiple times? Are there certain times in the day when you have a harder time focusing? Think about what time of day you are motivated to do things and plan to tackle harder tasks when you feel most productive. If there are certain times in the day when you feel like your energy is drained, plan for a walk at that time (ideally outside.) Exercise can also be planned at a time when you feel most up for it.

How to sync your circadian rhythm:

  • Ensure you are getting plenty of light in the morning. Ideally, this is upon waking up and throughout the morning into lunchtime.
  • Eat, sleep, and exercise around the same time each day. Your rhythm is synchronized with the environment and expects a routine.
  • Once it gets dark outside, limit artificial light exposure. Set phones and computer screens to automatically go to “night mode” or use blue light blocking glasses. Turn off or dim lights in the evening and avoid using LED light bulbs as they emit more blue light. Since our bodies do not recognize the difference between artificial light and sunlight, this will prevent unwanted melatonin suppression and cortisol synthesis. 
  • Eat during daylight hours. For example, 10-12 hours to eat and 12-14 hours to fast. You may fast longer if you like for additional health benefits! This helps to optimize circadian homeostasis in the gut microbiome. Calorie extraction and metabolism are positively impacted, therefore leading to better weight management. 

Potter GD, Skene DJ, Arendt J, Cade JE, Grant PJ, Hardie LJ. Circadian Rhythm and Sleep Disruption: Causes, Metabolic Consequences, and Countermeasures. Endocr Rev. 2016;37(6):584-608.
Bishehsari, F., Voigt, R.M. & Keshavarzian, A. Circadian rhythms and the gut microbiota: from the metabolic syndrome to cancer. Nat Rev Endocrinol. 2020;16,731–739.
Li Y, Hao Y, Fan F and Zhang B. The Role of Microbiome in Insomnia, Circadian Disturbance and Depression. Front. Psychiatry. 2018;9:669.
Marc Wittmann, Jenny Dinich, Martha Merrow & Till Roenneberg. Social Jetlag: Misalignment of Biological and Social Time, Chronobiology International, 2006;23:1-2, 497-509.

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