Why Circadian Rhythm matters

Have you ever locked yourself in your apartment for a whole day - or more - oblivious to the daylight or time of day? If you're anything like me, my introverted-self still seems to follow an internal clock that makes me go to sleep around 10pm. I'll hit deep sleep around 2pm, and my body will start to warm up around 4am anticipating waking up around 7am. My melatonin hormones drop as my stress cortisol hormones increase to take on the new day becoming most alert around noon. My peak reaction, coordination and muscle performance occur in the late afternoon. Unaware as it becomes dark, my body prepares for sleep around 10pm by increasing melatonin and cooling my body temperature. This all happens without us paying much attention to the time or daylight due to our built in circadian rhythm.

  • Circadian rhythm is our internal 24-hour clock modulating the brain, body, hormone secretion, cellular function and gene expressions [3][4][5] as we cycle between sleepiness and alertness at regular intervals. 
  • Melatonin is a hormone that is produced by the pineal gland in animals and regulates sleep and wakefulness [6].
  • Cortisol is a steroid hormone produced by the adrenal gland, a multi-steroid hormone producing gland. Cortisol is released in response to stress (waking up) and acts to increase blood sugar, suppress the immune system, and aid in metabolism [7].

Circadian Rhythms (CR) are evolutionarily built into not just humans but all living organisms. From a biochemistry perspective circadian rhythms are involved in metabolism (how we digest food), mitochondrial function (how we create and burn energy), and autophagy (how our bodies clean house on a cellular level). 

For further explanation of Circadian Rhythm read a 5 minute breakdown [25] or watch a 5 min video [26].

Although your internal clock adheres to a regular 24-hour rhythm, it can be manipulated or confused by our environment. Light exposure and eating times seem to be the largest regulators, but food type, noise, temperature, physical exertion, and sleep quality can all play a critical role in maintaining a healthy circadian rhythm.


It's good to understand we have this internal watchmaker AKA Circadian Rhythm, but why does it matter? Like any good young-professional, frequently staying up past midnight, constantly snacking, and binge watching Netflix can become the norm.

Can we continue to depend on coffee and soda to cure our lack of sleep and still successfully meet all of our boss's/customer's expectations ... I'll let you answer that one. 

The literature continues to stack up on the importance of understanding and minding our circadian rhythm. It is hard to miss the news when the Nobel Prize in Physiology or Medicine 2017 was awarded to the discoveries of molecular mechanisms controlling circadian rhythm [3]. These genetic mechanisms are proving how the previously observed health effects and conditions arise when our biological clocks are disrupted.

Studies repeatedly show the consequences of disrupting CR, such as obesity, accelerated aging, metabolic syndrome #comingsoon, diabetes, depression/anxiety, surgery recovery, UV damage, and cancer risk to name a few [R].

  • Night shift workers tend to have a higher prevalence of overweightness, abdominal obesity, elevated triglycerides, dyslipidemia, impaired glucose tolerance, and decreased kidney function compared to day workers [9].
  • Disrupting melatonin, the sleep hormone, can result in depression, sleep disorders, eating disorders and age-related dementia [15]. Melatonin is affected by the blue light spectrum from overhead lights, phones, TV's.
  • Artificial lighting enabled a 24-hour active lifestyle disrupting our natural daily cycle of eating (and eating more) chronically contributes towards diabetes, obesity, heart disease and accelerated aging by not proper cycling hormones and our metabolism [23].
  • Late night eating offsets the gut's microbiota temporal cycle required for proper metabolism of foods, immune responses and inflammatory responses which can contribute to a variety of conditions including asthma, obesity, colitis and colon cancer [24].
  • 70% of FDA drugs are less effective or more effective at certain times of the day subject to circadian effects [8].

It seems obvious that light sources can affect our circadian rhythm, but the work on time restricted eating is proving to be even more beneficial than the type of food you ingest. 

"What is interesting is, light is not the only thing that resets our clock. When it comes to the rest of the body, it's the time when we eat that is actually more important."

Dr. Satchin Panda via TEDxYouth [4]

To add another layer of complexity, it turns out eat-time may become increasing important as we age due to a receptor in the brain used to transmit light information becomes less effective in resetting the circadian clock [19].

Our goal at Bachelor.Fitness is to greatly lower our risk of these diseases and medical conditions. Action is on each of us individually to identify our flaws disrupting the circadian rhythm and implement the fix!


Now understanding the importance of maintaining a solid circadian rhythm, you're probably wondering what pill/supplement can you purchase or health-hack can you implement. There is no magic pill, but there are quite easy tips and tricks to ensure a healthy internal clock. 

Surface level all these may seem easy and obvious, but you'll figure out quick that it's hard to put down your phone at a good hour before bed or escape that nighttime snack (or night-cap beverage).

  • Sleep better - set your bedtime around 11pm and wake-up time at 7am enabling 7.5hrs of sleep to hit all sleep-cycles #comingsoon [17]. Ensure you minimize all noise, thermostat set to 60-65F, and zero light in your bedroom.
  • Time restricted eating (TRE) - also known as intermittent fasting, eat within a 10 hour window of the day only drinking water outside of that window. Try foregoing early-breakfast and starting your clock around 11am with early lunch. This gives you until 9pm to finish dinner. Ideally this give you 2-3 hours of no-eating prior to bedtime of 11pm [8]. Earlier TRE cycle enables lower morning blood glucose levels (high glucose levels => risk of diabetes) [12] [23].
  • Maximize natural sunlight - go outside and shoot for a 30 minute dose of sunlight helping secure your wake-cycle as well as getting recommended vitamin D. If you have can't get enough daily sunlight or work a night shift look into a therapy lamp for next-best thing to sunlight.
  • Minimize artificial light - no blue light 2 hours before bedtime. Preference no TV, phone or laptops. Use incandescent lightbulbs close to nighttime. Leverage nightshift-mode and Flux app for screen technology at night [14]. You may need black-out tape or electrical tape on your electronics that have stand-by lighting. Also, look into blue light blocking glasses/lenses [22].
  • Read old-school books - before bed read from paper books under dim yellow/red non-blue emitting light. Ereaders and light emitting devices disrupt our circadian rhythm and next day alertness as well as delays melatonin/REM [14].
  • Adjust your sleep-wake cycle - go camping for a long weekend to get on natures light cycle [13].
  • Caffeine - do not consume caffeinated beverages such as coffee or soda 4 hours prior to bedtime [11].
  • Exercise - physical activity is shown to be a driver of improving sleep, which has a a bidirectional relationship with exercise [16].
  • Wake up naturally - after you're on a good sleep-wake cycle use your body's internal clock to wake up naturally.
  • Nap - take naps if you can't get a full night's sleep or if you need to adjust to a better sleep-wake cycle.

Does this seem like a lot? Do you need a method to implement these behaviors? Our Rhythms training covers all this information and more.

To go beyond this high-level list, join our 6 week training and weekly blog where we aim to maximize your healthspan by diving into the details and prioritizing each step.

Staving off Metabolic Syndrome is why I continue down this fitness journey. Not only reaping the benefits later in life, but every day I stay dilegent with these health behaviors. Join us in this journey


[1] Meal Timing Regulates the Human Circadian System

[2] Circadian Rhythm Wikipedia

[3] 2017 Nobel Prize in Physiology or Medicine - Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discoveries of molecular mechanisms controlling the circadian rhythm

[4] How Your Circadian Rhythm Tunes Your Health: Satchin Panda at TEDxYouth@SanDiego 2013. "3 to 6 months old we develop internal clocks" - shine light in front of blind people disrupts their sleep cycle.

"What is interesting is, light is not the only thing that resets our clock. When it comes to the rest of the body, it's the time when we eat that is actually more important."

[5] National Sleep Foundation - What is Circadian Rhythm?. "A part of your hypothalamus (a portion of your brain) controls your circadian rhythm. That said, outside factors like lightness and darkness can also impact it. When it’s dark at night, your eyes send a signal to the hypothalamus that it’s time to feel tired. Your brain, in turn, sends a signal to your body to release melatonin, which makes your body tired. That’s why your circadian rhythm tends to coincide with the cycle of daytime and nighttime (and why it’s so hard for shift workers to sleep during the day and stay awake at night).

Your circadian rhythm works best when you have regular sleep habits, like going to bed at night and waking up in the morning around the same times from day to day (including weekends). When things get in the way, like jet lag, daylight savings time, or a compelling sporting event on TV that keeps you up into the wee hours of the morning, you can disrupt your circadian rhythm, which makes you feel out of sorts and can make it harder to pay attention ."

[6] Melatonin Wikipedia. Definition

[7] Cortisol Wikipedia. Definiton

[8] Dr. Satchin Panda on Practical Implementation of Time-Restricted Eating & Shift Work Strategies. "The revelation that 70% of FDA drugs are subject to circadian effects and are either less effective or more effective at certain times of the day ... The effect melatonin has on the pancreatic production of insulin and the insight this lends to why we should probably stop eating at least 2-3 hours before we go to bed ... circadian rhythms affects everything from susceptibility to UV damage to recovery from surgery to cancer risk" 

[9] Impact of nightshift work on overweight and abdominal obesity among workers of a poultry processing plant in southern Brazil. "For example, it has been shown that night shift workers tend to have a higher prevalence of overweightness, abdominal obesity [20], elevated triglycerides, dyslipidemia, impaired glucose tolerance [21,22,23,24,25], and decreased kidney function [26] compared to day workers."

[10] The Health Impact of Nighttime Eating: Old and New Perspectives. "those with NES (nighttime eating syndrome - consuming a large percentage of total daily calories after dinner) have higher 24 h respiratory quotient indicative of greater carbohydrate oxidation and less fat oxidation [35] compared to those without NES"

[11] Effects of caffeine on the human circadian clock in vivo and in vitro. "we found that consumption of a caffeine dose equivalent to that in a double espresso 3 hours before habitual bedtime induced a ~40-min phase delay of the circadian melatonin rhythm in humans. This magnitude of delay was nearly half of the magnitude of the phase-delaying response induced by exposure to 3 hours of evening bright light (~3000 lux, ~7 W/m(2)) that began at habitual bedtime."

[12] Effects of a late supper on digestion and the absorption of dietary carbohydrates in the following morning. "The mean blood glucose level under late suppertime conditions was significantly higher than under usual suppertime conditions.. Having a late supper showed a worse effect on postprandial serum glucose profiles the following morning. This study confirmed that keeping our usual meal timing is important for our health."  "Having a late supper showed a worse effect on postprandial serum glucose profiles the following morning."

[13] Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle. 1 week of camping reset all participants circadian rhythm with the natural light cycle. 

[14] Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. "We found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning."

[15] Why Is Blue Light before Bedtime Bad for Sleep? Scientific American.

[16] The bidirectional relationship between exercise and sleep: Implications for exercise adherence and sleep improvement

[17] Brain Basics: Understanding Sleep - NIH National Institute for Neurological Disorders and Stroke . 

[18] Timing of light exposure affects mood and brain circuits.  

[19] Why we struggle to get good night's sleep as we get older.  "They found that a glutamate receptor (NMDA), used to transmit light information, became less effective in resetting the circadian clock as part of the aging process."

[20] Aging is exacerbated by alterations of stem cell circadian rhythm

[21] The link between circadian rhythms and aging: Gene associated with longevity also regulates the body's circadian clock

[22] Artificial light from digital devices lessens sleep quality. 

[23] Fasting, circadian rhythms, and time restricted feeding in healthy lifespan

[24] Circadian rhythms and the microbiome: Disrupting daily routine of gut microbes can be bad news for whole body


[26] Circadian Rhythms and Your Health Video - Brigham and Women's Hospital - YouTube