Circadian rhythms are 24-hour cycles driven by your body’s internal time clock. Like an alarm clock, this clock runs continuously and signals your body to carry out essential processes and functions.

For example, a critical, but often taken-for-granted circadian rhythm is your “go to sleep-wake up” cycle. This particular cycle seems simple, but it is a complex process with many functions going on in parallel but in a strictly monitored distinct series of steps.

Sleep and wakening is something we do every day, and it is, without doubt, one of the most important times of the day for our body’s rejuvenation and repair.

Your brain controls circadian rhythms.

How does your body seem to know the time of day? The Suprachiasmatic Nucleus (SCN), a small cluster of cells in your hypothalamus, sense light and dark signals. When your eyes encounter light, your retina sends a signal to your SCN. The SCN sets off a chain reaction of hormones and signals to affect body temperature, appetite, sleep drive, and more.

This ongoing monitoring process is primarily guided by light, especially the sunlight that triggers many of your bodily functions. This little cluster of cells, the SCN, is in the middle of your brain, slightly behind your optic chiasma.

Now, I don’t want to get into a lot of neuroanatomies, so here are two simple illustrations of the SCN’s position inside your brain taken from the top and side of your head.

Circadian rhythms are managed by the SCN - this illustration shows you it's location in relation to your skull and eyes.

Suprachiasmatic means “just above the optical chiasma where the optic nerves cross.

This puts the SCN inside your brain about a third of the way from your forehead to the back of your head.

This is where your hypothalamus is (see illustration below).

Hypothalamus and SCN:

Circadian rhythms involve your retina and the SCN in your hpothlmus. This illustration shows their close nexus at age optic chiasm.
Human Brain Illustrating SCN Relation to Hypothalamus

Although this illustration is not as clear as I would like, it is sufficient to show you the relationship between the SCN, the optic nerve, and the hypothalamus. This anatomical relationship is important to understanding circadian rhythms.

These rhythms are driven by light and especially sunlight. It is no accident that we have an internal clock that works in a 24-hour timeframe. This is our evolutionary heritage expressed in neurological terms.

The optical chiasm is where nerves from our retinas cross behind our eyes. This is a point where lots of things are going on. One of these things is a signaling set of nerves from the chiasm to the SCN in the hypothalamus.

Now, it’s pretty easy to see their physical relationship in the illustration.

So here’s the sequence: light falls on your retinas, a signal is sent to your SCN, and it is processed by the hypothalamus, which sends signals to the appropriate centers in the brain.

It’s very complex, and what I gave you is the OMY1 tour. This article is not about neurology, but a little explanation is necessary.

So about circadian rhythms:

Sleeping is a classic example of a circadian rhythm. For hundreds of thousands of years, mankind and other animals lived according to the 24-hour cycle of the sun. This cycle is why you get tired and sleepy when the sun goes down, and why you naturally wake up when it comes up.

For four years now, I have followed the sun with my sleeping habits. When the sun goes down, I begin my bedtime preparations and go to bed. When the sun comes up, I awaken naturally. I do not use clocks for this, my body is well aware of the times, and everything is almost automatic.

I seldom have sleep problems.

Now I know not everyone has these options, but to the extent possible, study your body’s reaction to light (especially sunlight) and try to work within its rhythms as much as possible. This is especially true if you have sleep problems that are not caused by an external force.

Other circadian rhythms:

Hunger might be a circadian rhythm and partly a habit. Thousands of years ago, eating was a “gorge when you find it” behavior, and the search for food was a full-time activity. Now, we have been habituated to three meals daily, but this is also timed with the 24-hour internal clock.

This leads to the speculation that habits are quasi-circadian behaviors, and this is why they’re so hard to break.

There are also certain times in a day when we feel tired, or listless. We know when we are ready to get off work and when it’s the weekend. We know these things without looking at the clock or a calendar.

Time for us is always a 24-hour-a-day fact of life. This is why astronauts and others insulated from the 24-hour cycle need signals to mark times in their days. This is true also of prisoners held in dark rooms for long periods of time, and deprived of the 24-hour cycle develop mental and physical problems.

Bodily functions:

Most of the time, you do not need to urinate or defecate in the middle of your sleep. Your brain turns these functions off during sleep. Other things happen too. Digestion slows down, and blood pressure changes. So does respiration.

They also increase when you wake up. Almost always, we have to urinate when we get up in the morning, and defecation often goes along with the same general timeframe. Our respiration gets deeper and faster, and our blood pressure and heart rate increase.

Lots of other things are going on as well. We don’t think of these things; they just happen. Now not everything is circadian; some things are routines and habits. Our bodies adapt to these things, and they become neurologically and physiologically anticipated events as well.

A fascinating study about cancer treatment:

Chemotherapy’s success is affected by the time of day.

Let’s take a look, but before we discuss this, here’s the relevant study link for those of you who want more information.

Women with diffuse Large B-Cell Lymphoma had far better outcomes when they received chemotherapy in the afternoon instead of the morning.

Cancer treatment timing is being examined in more detail. The treatment success differential is tied to our daily circadian rhythms driven by the sun and managed by the circadian clock.

Chemotherapy timing and outcomes.

Researchers looked at two groups of patients, the first treated at 8:30 in the morning and the second at 2:30 in the afternoon. All patients received chemotherapy (a regimen called R-CHOP) four to six times at intervals of three weeks.

When compared to Women given chemotherapy in the morning, those given chemotherapy in the afternoon had considerably longer progression-free survival, and their overall survival was greater as well.

The morning group had a 25% mortality rate compared to 2% in the afternoon group, and a 24% higher 5-year recurrence rate.

See more here: Michael Hunter, MD.

My Comments:

These results are striking. There is no way these differences are insignificant. The reason I included this study is to illustrate the extensive integration of circadian rhythms into our biology.

It is utterly masterful how light, especially sunlight, sets the pace for our daily lives, including our thinking and physiology. We truly are children of the sun (thanks, Billy Thorpe).

“The human body can think through thoughts, play the piano, kill germs, remove toxins, and make a baby all at once. Once it’s doing that, your biological rhythms mirror the universe’s symphony because you have circadian, seasonal, and tidal rhythms that mirror everything happening in the universe.” — Michio Kaku

Final thoughts:

Following the cycles of the sun is critical to our health. I know that all of us can’t do this faithfully because of our situations. But to the extent possible, try to match your behaviors to the 24-hour sun cycle.

Not doing this can be harmful:

People living in geographies with extended dark and light periods are more prone to suicide.

People working night shifts and especially swing shifts are prone to having more health problems.

Prisoners in solitary confinement and denied access to sunlight and the 24-hour life cycle are mentally and physically unhealthier than those prisoners who aren’t.

These are facts that show a clear possibility of harm from a lack of sunlight and removal from the 24-hour sun cycle. This might result partially from sleep disruption (which is circadian), but as we’ve learned, the effects of sun cycling are far more subtle and far-reaching than we imagine.

Ancient mankind worshiped the sun and lived by its cycles. Maybe they weren’t all that far off. God’s greatest gift to the world might be the sun.

OMY1

For additional information on following the sun, see this article:

Note: this article will appear in my Planned Longevity™ Strategies.

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