Circadian Rhythm – What it is and Four Ways to Support It

August 15th, 2021

August is back-to-school month for many students and families. Leisurely downtime typically lessens, and life becomes a bit more chaotic with work, school, social activities, and everything in-between. Consequently, diet, exercise, and sleep might change as events pile on the calendar.

However, what are the metabolic health risks of such lifestyle changes?

As functional nutrition practitioners, we know that metabolic health is influenced by various factors, including genetics, diet, lifestyle choices, and circadian balance.

A well-supported circadian rhythm, in particular, is critical for sound sleep, energizing metabolism, cognitive function, and disease risk reduction.

Let’s dive into circadian rhythm specifics and go over four practical strategies to support circadian rhythm when life gets crazy.


What is Circadian Rhythm?

The word “circadian” is derived from the Latin terms “circa” (around) “diem” (day), so circadian rhythm literally translates to “around-the-day” rhythm (1).

A more scholastic definition of circadian rhythm is “the natural cycle of physical, mental, and behavior changes that the body goes through in a 24-hour cycle” (2).

Most people rightly associate circadian rhythm with the sleep-wake cycle. However, it is involved in various bodily processes, including energy homeostasis, cytokine secretion, glucose metabolism, renal activity, and hormone secretion.


How Does it Work?

Circadian rhythm, also known as the body’s master clock, is biologically connected to daily environmental cues. Such cues are known as “zeitgebers.” The light/dark cycle is the most impactful zeitgeber, but other stimuli like exercise, meal timing, social activities, and temperature are also important (3,5).

The suprachiasmatic nucleus (SCN), a small area in the hypothalamus, controls circadian rhythm by responding to lightness and darkness. Light exposure stimulates receptors in the retina, triggering a domino effect of signaling from the SCN of the brain to peripheral tissues. According to Yanling et al., all cells in the human body and roughly 10% of the genes expressed in tissues are synchronized with the SCN (4).


Cortisol, Melatonin, and Circadian Rhythm

Many hormones fluctuate throughout the 24-hr circadian cycle. Cortisol and melatonin, in particular, play an essential role in the sleep-wake cycle, metabolism, stress response, and overall circadian balance.



Under healthy circumstances, cortisol level peaks in the morning, declines throughout the day, is lowest in the evening, and slowly rises overnight. A disruption in cortisol rhythm can lead to restless sleep, inadequate stress response, and increased pro-inflammatory proteins, TNF-α and CRP (6).



Melatonin and cortisol have an inverse relationship. Under healthy circumstances, melatonin is lowest in the morning, increases throughout the day, is highest in the evening, and slowly declines overnight.

Melatonin production is significantly impacted by light exposure. The physiology is pretty straightforward: as the sun sets, the SCN signals the pineal gland to produce more melatonin, promoting rest and sleep. When the sun comes up, the SCN signals the pineal gland to slow down melatonin production, preparing the body for the day ahead.

Beyond sleep, melatonin is an immune-supportive antioxidant that possesses anti-inflammatory and neuroprotective benefits. It is also being used as a possible way of protection in many diseases, including cancer (7). Furthermore, a 2011 review in the Journal of Physiology and Pharmacology revealed a connection between disrupted circadian rhythm and melatonin production, and the onset of gastrointestinal diseases like GERD, peptic ulcer disease, and IBS (18).


Circadian Disruptors

Many lifestyle factors can negatively impact circadian balance, specifically stress, poor sleep hygiene, and a nutrient-deficient diet.



Stress and circadian rhythm have a bi-directional relationship. Circadian disruption can impact an individual’s ability to cope with stress. Conversely, both chronic and acute stress can negatively impact circadian rhythm.

Repeated or long-lasting stressful situations are most damaging to circadian balance because it chronically alters the body’s stress response system, i.e., HPA axis and cortisol rhythm. Furthermore, chronic stress stimulates gluconeogenesis and glycolysis in the liver while simultaneously reducing glucose utilization in peripheral tissues. This leads to elevated blood glucose, insulin secretion, and dysregulated circadian balance (12).



Poor sleep hygiene is a significant circadian disruptor. Chronic lack of sleep can lead to various adverse health effects like mood disorders, decreased cognitive and memory function, obesity, elevated cortisol, increased inflammatory markers, insulin resistance, and disrupted glucose metabolism (8, 9).

Common sleep interferences include:

  • Excessive evening blue light exposure
  • Excessive evening noise
  • Alcohol intake*
  • Overconsumption of caffeine
  • Sleep apnea
  • Jet lag
  • Shift work (9)

*An important note on alcohol intake: there is a wide held belief that an evening nightcap helps promote restful sleep. Even though it might make a person feel sleepy, it reduces melatonin production by nearly 20%, consequently disturbing the sleep-wake cycle and circadian rhythm (10).



Studies show that what and when we eat impacts circadian rhythm. There are several diet-related circadian disruptors:

  • Alcohol
  • High saturated fat intake
  • Trans fats
  • Caffeinated foods and beverages
  • Simple sugars
  • Ultra-processed foods
  • Late-night eating (11)


Four Tips to Support Circadian Rhythm


Time-Restricted Feeding (TRF)

The circadian clock is influenced by not only what we eat but when we eat. In fact, frequent eating and the absence of fasting can interfere with metabolic pathways that help regulate the body’s circadian rhythm. Studies show that a feeding-fasting cycle, like TRF, is a great way to support circadian balance (13).

Fasting and time-restricted feeding offer many benefits. For example, a few hours of fasting activates AMP-activated protein kinase (AMPK) (13). AMPK regulates autophagy, repair, and catabolic processes necessary for mitochondrial health (14). Furthermore, fasting and AMPK production positively affect specific genes that help regulate our circadian clock (13).

In Track 2/Module 5, Dr. Mark Pettus recommends a 10-hour eating window during the day and a 14-hour fasting window overnight to help support circadian rhythm.


Focus on the Mediterranean Diet Principles

A plant-forward Mediterranean diet offers many benefits, like reducing the risk of heart disease, cancer, and overall mortality. Recent findings suggest that the Mediterranean diet is also beneficial for circadian rhythm support.

A 2017 study evaluated a Mediterranean Diet rich in extra virgin olive oil and its impact on specific circadian clock genes. Results showed that terpenes, specifically oleanolic acid, found in EVOO are essential modulators of genes involved in circadian balance (15). A separate 2019 study found that in-season fruits and vegetables also offer circadian support via polyphenolic compounds (16).


Reduce Evening Light Exposure

Establishing an evening routine can offer many benefits, the most obvious being quality sleep. In today’s tech-driven world, light exposure can be a significant sleep disruptor due to its ability to interfere with melatonin production. Studies show that dimming phone screens, using warm, orange-hued lights, and wearing blue-light-blocking glasses 3-4 hours before bed can help support the body’s natural melatonin production (17). The ultimate strategy, however, is putting all gadgets away in the evening.


Fill in the Gaps with Supplements

Supplements, while not required, can be a helpful addition to a whole foods diet to maintain circadian balance. Adaptogens, for example, can help the body respond to varying degrees of stress by promoting homeostasis, thus supporting circadian rhythm. Magnesium, melatonin, GABA, L-theanine, lavender, and chamomile may also be recommended to support stress reduction, sleep, and circadian rhythm.



Circadian balance is critical for overall health and well-being. There are several ways to support circadian rhythm from a functional nutrition lens, many of which are discussed in the IFN Academy training program. Sign up today to learn more!


by Tori Eaton, RDN, IFNCP


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