Rest assured when you know your internal body clock

What is an internal body clock and circadian rhythm?

The idea that we have an internal body clock was first noticed in the 18th

century by French scientist Jean-Jacques d’Ortous de Mairan who noticed that

plants that kept steady temperatures in a dark space also continued their

daily rhythm of opening and closing their leaves. De Mairan thought that this

was because plants sense sunlight without ever seeing it”(1).

The term “circadian” comes from the Latin words “circa” which means “about” and 

“diem” (day)– and together, the words mean “about a day”.  The term,

described by Romanian biologist Franz Halberg in 1959,

found that circadian rhythms are in part, endogenous, meaning they work

internally) and they can be manipulated by outside factors, such as the

ce of light.   Circadian rhythms which are present in humans, plants,

animals and marine life, help regulate the body to attune with

different parts of the day. Changes in length of daylight inform the body what to do. 

In an article about circadian rhythm, neuroscientist, Louis Ptacek, MD,

Professor of neurodegenerative diseases, UCSF, Weill Institute for Neurosciences

describes how light and darkness control our internal bod

y clock, and he explains it as “the 24-hour cycle of waking and

sleeping in response to daylight and darkness. When you’re sleeping and

the sun comes up, your eyes sense the light even when they’re closed. That light s

ends a signal to your brain signaling you to wake up.” Your body gets ready for

the day by awakening your digestive and immune systems, raising blood pressure, etc.  

When night falls, our bodies know to reverse this process.” [2}] 

How does this happen? 

Research into the science of circadian rhythm and internal body clock

is explained by the ways in which a cluster of approximately

20,000 cells in our brains, called the suprichiasmatic nucleus cells,

SCN) regulate the different biological roles in our bodies, including our sleep

and wake our metabolism and digestion. Interestingly, environmental

factors, such as light have one of the most powerful effects on our

circadian rhythms. Light is taken in by the retina of the eye and then

cells send information to the pineal gland and other parts of the

brain telling it to stop producing the hormone, melatonin, which plays a key

role in helping us to sleep.  (3)

How Disruption to Circadian rhythm causes problems with sleep 

When your body’s internal clock is disrupted, your body’s natural rhythm

(circadian rhythm) is thrown off balance. potentially causing a variety

of difficulties, including short-term effects like problems sleeping, fatigue, and

trouble concentrating, as well as longer-term health issues such

as weight gain, and more serious conditions, including mood disorders. In addition,

we know that light, and lack of light especially in the Fall and Winter

months can cause a variety of mood difficulties and depressive

symptoms, including Seasonal Affective Disorder (SAD).  Importantly, it is

thought that a major component that triggers all mood disorders, including SAD,

major depressive disorder (MDD), and bipolar disorder (BD) are partly

triggered by disruptions to the sleep and wake cycle [4]

Because of this, prioritizing sleep is paramount for good self care

and it’s especially important during the Fall and Winter months when we

turn the clocks back and get less natural light.  Karin Johnson, a neurobiology

professor at the University of Massachusetts Chan School of Medicine and

a member of the American Sleep Medicine Advocacy Committee states

that when we pay attention and sync our activities to align with 

natural light patterns of the day and night, we will have better

quality of sleep as well.  This view aligns with those of the American Academy of Sleep 

Medicine (AASM), American Academy of Neurobiology

and the health and safety-focused non-profit, National Safety Council.   

Ways to naturally optimize your sleep and support your internal body clock

—Get morning light.

—Avoid blue light from screens, especially at night.  

—Exercise, but not too close to your bed time.

—Try to eat meals at consistent times each day and not too late at night, if possible. 

—Limit caffeine and all substances that can impede sleep.  

—There is much on the topic of nutrition, but eating a nutrient-dense diet,

reducing sugar and increasing intake of whole, unprocessed foods will go a long way to

supporting your body’s natural internal rhythm. (5) 

—Seek help from a healthcare practitioner and consider behavioral therapy. 

If your mind is racing at night, or if you are suffering from anxiety and/or depression it

can be extremely difficult to relax enough to get a good night of sleep.

Menopause, and other hormonal shifts can also contribute to low mood and

lack of good quality sleep. Working with your health care provider to

identify any physical barriers to sleep is key, as well as working with your mental

health provider to address emotional symptoms of anxiety, depression,

and any trauma-related symptoms. 

According to the Mayo Clinic, sufferers with insomnia can be

effectively treated with behavioral therapy (6). The study cites cognitive behavioral

therapy as a way to treat long term sleep problems and is the first line

recommended treatment.  Other types of treatment such as

internal family systems therapy, often referred to as parts work is another model

that may prove to be beneficial.  Through a collaborative approach this model

helps you to identify parts, thoughts, or feelings that can disturb sleep.

For example, you could have anxious parts that stay up and try to process your

fears and worries at night, a depressed part that may sleep too much

during the day so that sleeping at night becomes difficult. Or you might even

acknowledge the productive parts that want you to keep working when it would be better

if you slowed down.  If you are having trouble with sleep due to anxiety or depression,

working with a therapist is time well spent and could help you to tune

into your internal system, teach you to ways to optimize and understand

your unique circadian rhythm, and lead you to to greater emotional and

physical well being.  

References: 

1) The birth of chronobiology: a botanical observation.

by Jonathan Sobel, PhD | Sep 23, 2019 | Clocks in the Spotlight

2) Why Is It So Hard to Adjust When Clocks ‘Fall Back’? | 

UC San Francisco. (2025, October 30)https://www.ucs

f.edu/news/2025/10/431001/why-it-so-hard-adjust-when-clocks-fall-back

3) What Is Circadian Rhythm? (n.d.). Cleveland Clinic. Retrieved November 9, 

2025, from https://my.clevelandclinic.org/health/articles/circadian-rhythm

4) Dollish, Hannah K., Mariya Tsyglakova, and Colleen A. McClung.  Circadian]

Rhythms and Mood Disorders: Time to See the Light.” 

Neuron 112, no. 1 (2024): 25–40. https://doi.org/10.1016/j.neuron.2023.09.023

5) Circadian Rhythm Disorders: Treatment

https://www.nhlbi.nih.gov/health/circadian-rhythm-disorders/treatment

6) Insomnia treatment: Cognitive behavioral therapy 

instead of sleeping pills. https://www.mayoclinic.org/dis