Master Clock Circadian Rhythm: What Happens When Your Body Is "Off Time?"

By Jennifer Wolff-Gillispie HWP, LC

Originally published by A Voice For Choice Advocacy on January 4, 2024.

“I have few absolutes in my routine, but one of them is this: I honor my circadian rhythm. The pleasure I get from consistently sleeping well trumps anything that would disrupt it.”

~ Mark Sisson, American fitness author, food blogger, and a former distance runner, triathlete and Ironman competitor

**This article was last updated on 08-30-25 (see below).
*This article was updated on 05-30-25 (see below).

Before the invention of electricity, most people rose with the sun each morning to go about their day. In the evening, as the sun withdrew from the sky, they retreated to their homes to retire. This was the sleep-wake cycle of humans for millennia. It wasn’t until the advent of electricity and the incandescent bulb, that people en mass began working into the night, aided by the bright light of electric lamps.

Your life is inextricably tied to the natural world around you. The cycle of photosynthesis provides plants with carbon dioxide they need to grow, while allowing you the oxygen necessary to breathe. The cycles of day and night may not seem connected to your existence in an obvious way, but as the importance of your body’s circadian rhythms are explored further, you will find otherwise.

National Institute of General Medical Sciences (NIH) describes circadian rhythms in this way:

“Circadian rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect most living things, including animals, plants, and microbes… Biological clocks are organisms’ natural timing devices, regulating the cycle of circadian rhythms. They’re composed of specific molecules (proteins) that interact with cells throughout the body. Nearly every tissue and organ contains biological clocks… 

A master clock in the brain coordinates all the biological clocks in a living thing, keeping the clocks in sync. In vertebrate animals, including humans, the master clock is a group of about 20,000 nerve cells (neurons) that form a structure called the suprachiasmatic nucleus, or SCN. The SCN is in a part of the brain called the hypothalamus and receives direct input from the eyes.”

Today you are bombarded by artificial illumination at all times. Neon signs, fluorescent lighting, T.V’s, computer screens, smart phones, street lights, and automobiles’ luminous emissions seem to be an unavoidable part of daily life. This “light pollution” (especially during the evening hours) can be detrimental to your health in many ways. Research by Harvard University had this to say:

“The amount of light entering the eye is key in helping our brain distinguish times for wakefulness and times for sleep. The SCN is highly sensitive to light exposure, as light provides an external cue for internal clock regulation. Exposure to artificial light disrupts our internal clock regulation. 

Upon light exposure, the SCN starts a signaling pathway that leads to a reduction in melatonin, the hormone responsible for regulating our sleep-wake cycle. Melatonin reduction results in daytime sleepiness and sleep disturbances. It may also modify our immunity and stress response. The amount of downregulation is dependent on the intensity and wavelength of light entering the eye. However, new research has found that even low light intensities from urban skyglow can cause melatonin downregulation.”

More than just disturbing your sleep and leaving you exhausted, disruption of your sleep-wake cycle may negatively affect your immune system. From the Journal of Clinical Investigation (JCI):

“Recent discoveries demonstrate a critical role for circadian rhythms and sleep in immune system homeostasis. Both innate and adaptive immune responses — ranging from leukocyte mobilization, trafficking, and chemotaxis, to cytokine release and T cell differentiation —are mediated in a time of day–dependent manner.” 

This means that the many complex parts of your immune system have biological clocks that are regulated by the natural cycles of day and night to function optimally. As more research is being done to look at how pivotal circadian rhythms are to overall health, scientists are finding how critical proper sleep hygiene is to prevent sickness and disease. 

Physical Health Disruption

This research takes a look at various aspects connecting misaligned sleep-wake cycles to imbalance in the body, including how illness and disease are influenced.

Cancer

“Roles of circadian clocks in cancer pathogenesis and treatment,” posted in Experimental & Molecular Medicine (EMM), looked at the connection between cancer and circadian rhythms:

“Disrupted circadian rhythmicity has been a prominent feature of modern society since the invention of artificial light sources. Indeed, 80% of the world’s population is now exposed to light during the night, and approximately 18–20% of workers in the USA and Europe are involved in night or rotating shift work, making them vulnerable to multiple rhythm disorders, including cancer. 

Several epidemiological studies further suggest that night shift work or chronic jet lag increases the risk of the incidence and development of the most common cancer types (i.e., breast, lung, prostate, colorectal, and skin cancers).”

From University of Rochester Medical Center, “What Happens if Your Circadian Rhythms are Out of Whack?”:

“The latest research, published in the high-impact journal Science Advances, describes that when the circadian clock gets off track it implicates a cancer-signature gene known as HSF1 that can trigger lung tumors. Lungs are under tight circadian control and seem to be particularly vulnerable to a disrupted biological clock.”

Obesity and Diabetes

In an article titled, “Disruption of circadian clocks has ramifications for metabolism, brain, and behavior,” from Proceedings of the National Academy of Sciences (PNAS), changes in metabolic hormones linked to circadian rhythms were explored:

“The relationship between circadian rhythms and metabolism is becoming an increasingly important area of research, and findings linking sleep loss and obesity are becoming increasingly numerous. Our findings demonstrate that chronic housing in a shortened LD cycle results in the alteration of body temperature rhythms, weight gain, and increases in both plasma leptin and insulin levels. The significance of these changes in metabolic factors is unclear, but both leptin and insulin are key hormones in the regulation of fat stores and glucose metabolism.”

Another study from nature reviews endocrinology, “Circadian clocks and insulin resistance,” went on to explain in further detail: 

“The circadian timing system is responsible for the coordination of many daily processes, including the daily rhythm in human glucose metabolism. The central clock regulates food intake, energy expenditure and whole-body insulin sensitivity, and these actions are further fine-tuned by local peripheral clocks. 

For instance, the peripheral clock in the gut regulates glucose absorption, peripheral clocks in muscle, adipose tissue and liver regulate local insulin sensitivity, and the peripheral clock in the pancreas regulates insulin secretion. 

Misalignment between different components of the circadian timing system and daily rhythms of sleep–wake behaviour or food intake as a result of genetic, environmental or behavioural factors might be an important contributor to the development of insulin resistance.” 

Gut Microbiome

The American Society For Microbiology, in their research titled, “Bacterial Circadian Rhythms: From Lakes to the Gut” examined the links between gut bacteria and circadian rhythms:

“The identification of circadian rhythmicity in gut-associated bacteria is intriguing in light of research showing that the gut microbiota exhibits daily oscillations in its composition. That is, the abundance of certain taxa peaks during one part of the day (morning) then crashes in another (night). 

These changes are influenced by Zeitgebers (different circadian periods in various light-dark cycles) associated with host circadian processes, as illustrated by melatonin-mediated synchronization of K. aerogenes (bacteria) rhythmicity. This underscores the close relationship between host and microbiota, in which processes in one (e.g., circadian rhythms) regulate and are regulated by the other.”

Put simply, your sleep habits, diet, and anything else that could disrupt your circadian rhythm will also disrupt your gut microbiome. These disruptions are linked to negative health consequences, including obesity and type 2 diabetes. In fact, your whole digestive process is regulated by a proper functioning circadian rhythm. 

According to Gastro Hep Advances in their study titled, “Circadian Rhythms, the Gut Microbiome, and Metabolic Disorders,” your internal clock plays an integral role in preserving metabolic homeostasis: 

“A variety of functions throughout the gastrointestinal tract and liver are under circadian control, including nutrient transport, processing, and detoxification. The gut microbiota also plays an essential role in host metabolism, regulating processes such as digestion, inflammatory modulation, and bile acid metabolism. Both the circadian clock and the gut microbiota influence each other in a reciprocal fashion, as gut dysbiosis can precipitate circadian asynchrony, and vice-versa. 

Disruption of either system impacts homeostasis in a bidirectional manner and can contribute to metabolic dysfunction. Evidence suggests such disruptions can lead to the development of metabolic diseases, including obesity, diabetes, nonalcoholic fatty liver disease, cirrhosis, and hepatocellular carcinoma.”

**UPDATE: 08-30-25
Cardiovascular Health

In the A Voice for Choice Advocacy article “Moving the Bar: The Evolution of Cardiovascular Health Standards and the Impact of Lowered Risk Markers on Public Health,” the connection between circadian misalignment and cardiovascular health is explored. It states:

“Supporting this natural cycle [circadian rhythm] by getting regular sunlight in the morning, maintaining consistent sleep and wake times, and avoiding bright lights at night can help keep your blood pressure, heart rate and stress hormones in check, reducing the risk of heart disease.”

Further demonstrating this connection, a 2023 study titled “Circadian Rhythms in Cardiovascular Function: Implications for Cardiac Diseases and Therapeutic Opportunities” highlights that cardiac disorders—particularly arrhythmias and myocardial infarctions—are strongly linked to circadian disruption. In fact, research shows a 40 to 63 percent increased risk of cardiovascular conditions associated with these disturbances.

Mental Health Disruption 

The following research takes a look at aspects connecting off-kilter circadian rhythms to imbalance in mood, including the influence on depression.

From the Depression and Bipolar Support Alliance (DBSA), in an article titled, “How Circadian Rhythms Impact our Mental Health”:

“If you live with depression or bipolar disorder, you likely have a more sensitive body clock, or circadian rhythm, meaning adjustments to time of day and differences in light can have a great impact on your mood. For example, we see this phenomenon with Seasonal Affective Disorder. As the days shorten in the winter, we know some people tend to experience heightened symptoms of depression because of the shorter amount of light exposure in a given day.”

From Nature: Translational Psychiatry, in their article titled, “Circadian rhythm disruption and mental health,” their research makes the link between circadian rhythms and mental health disorders: 

“Human clinical data support a strong interaction between MDD (Major Depressive Disorder) and circadian processes. Symptoms of depression demonstrate diurnal variations; patients exhibit symptoms in a morning-worse or evening-worse pattern. Patients with MDD typically express more severe symptoms in the morning, which is considered to be associated with a more severe form of depression. 

Disruptions of biological rhythms underlie hallmarks of MDD; specifically, alterations in sleep/wake states (decreased latency to rapid eye movement sleep, concurrent with increased rapid eye movement sleep and reduced slow wave sleep), social rhythms, hormone rhythms (reduced amplitude in melatonin and cortisol rhythms), and body temperature rhythms (reduced amplitude and increase in nocturnal body temperature) are seen in patients with MDD. Clinical studies demonstrate that the severity of MDD is correlated with the degree of misalignment of circadian rhythms.”

There are many contributing factors that can cause circadian rhythm dysfunction: Jet lag, working night shifts/ irregular shift changes, poor sleep hygiene (proper routine and habits around bedtime), brain damage, blindness, lack of sunlight, certain medications, and age. 

Another lesser known cause of circadian rhythm disruption is caused by electromagnetic frequencies (EMFs) and blue light that are generated by wireless and electronic devices, such as wifi routers, cell phones, computers, and televisions. EMF’s are thought to interfere with production of melatonin in the pineal gland because the brain receives the EMF’s and interprets them as light.

This disruption comes about because your brain interprets wireless signals (and pulsed microwave and radio frequencies) as a form of “bright light” which shuts down melatonin production. When your circadian rhythm is disrupted, you may begin to experience insomnia, feelings of being “stressed,” poor performance, difficulty waking, exhaustion throughout the day, depression, irritability, and sadness.

To avoid unwanted health issues, and reset your circadian rhythm, it's important to develop healthy sleep-wake habits. Here are a handful of ideas to consider:

• Choose a bedtime and wake time and stick to them (even on weekends). 

• If you need to take a nap, limit it to a 10–20 minute “power nap” in the early to mid-afternoon to avoid disruption of your circadian rhythm. This short duration and timing will allow you to retire in the evening on time.

• Commit to a regular exercise routine, and avoid exercise at least one hour before bed.

• Avoid alcohol, caffeine, and other stimulants at least a few hours before bed. (This is ideal, but perfection isn’t necessary).

• Get sunshine on your body as early in the day as possible (preferably within one hour of waking), and spend thirty minutes baking without sunglasses.

• Turn off the computer, T.V., smartphone, and any other artificial lights at least one hour before bed. 

• Your bedroom should be as dark as possible. Use blackout curtains, or try out a sleep eye mask.

Raising your awareness, and perhaps decreasing the time you spend with the constant surge of technology, i.e., the social media channels you've become accustomed to, may be pivotal in fostering an environment that is health-promoting. 

*UPDATE: 05-30–25
New research from the Norwegian University of Science and Technology discovered that common plastics used in food packaging—like cling wrap and snack pouches—may also disrupt your body’s natural circadian rhythm. This highlights how even minute, everyday decisions—ones that may seem unrelated—can have a significant impact on your health. Chemicals in common plastics like polyurethane and polyvinyl chloride were shown to disrupt signals that help regulate your sleep-wake cycle, delaying the activity of key body clock genes. While the study was done on lab cells, the results suggest that even small, regular exposures could gradually affect sleep, metabolism, and long-term health. Researchers are urging for safer materials and stronger regulations, warning that daily contact with these plastics may raise the risk of diabetes, immune issues, and cancer.

Making it a habit to get outside every morning to reconnect to the natural world, as well as settling in at night with a bath and book by candlelight, may be all you need to align your internal clocks, allowing you to sleep soundly, and awaken recharged and invigorated. 

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