Key PointsSeptember 16, 2026

• Nearly every cell in the body contains an internal circadian clock that helps regulate gene activity and coordinates hormones, metabolism, digestion, sleep and other physiological functions.
• Morning and daytime light help synchronize the body's master clock, while excessive bright and blue-enriched light at night can interfere with normal melatonin signaling.
• Chronic sleep restriction and circadian disruption are associated with impaired glucose regulation and other metabolic problems.
• When you eat may matter as well as what you eat. Research on time-restricted eating suggests that consistently avoiding late-night eating may support metabolic health.
• Regular sleep and wake times, daylight exposure, physical activity, appropriate meal timing and a dark bedroom are practical ways to strengthen circadian rhythms.
• Nutrients such as magnesium, vitamin D, B vitamins and omega-3 fatty acids may be appropriate when diet or testing identifies a need, but supplements should be individualized.

Your Body Runs on a 24-Hour Clock

We tend to think of sleep as something the brain does at night. In reality, the body's internal timing system extends throughout virtually the entire body.

Nearly every cell contains molecular clocks that regulate biological activity according to approximately a 24-hour cycle.

This affects much more than whether you feel sleepy.

Circadian rhythms influence melatonin, cortisol, body temperature, insulin sensitivity, digestion, appetite, immune activity, cellular repair and numerous other physiological processes.

Research into these biological clocks was considered important enough that the 2017 Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for discoveries concerning the molecular mechanisms controlling circadian rhythms. The source article discusses this work in detail.

The important lesson is simple:

Health is influenced not only by what we do, but also by when we do it.

Light Is One of the Body's Most Powerful Time Signals

For most of human history, bright light meant daytime and darkness meant nighttime.

Modern life has changed that dramatically.

We can now spend much of the day indoors under relatively modest illumination and then expose ourselves to bright lights, televisions, computers, tablets and smartphones late into the evening.

Specialized light-sensitive cells in the retina communicate with areas of the brain involved in controlling circadian timing and melatonin production.

This makes light exposure one of the simplest tools available for supporting a healthy circadian rhythm.

During the Morning and Day

Try to get outside and experience natural daylight, particularly earlier in the day.

Outdoor light is generally much brighter than ordinary indoor illumination. Morning light helps provide the brain with a strong signal that the biological day has begun.

Continue getting appropriate daylight and physical activity during the day.

During the Evening

As bedtime approaches, do the opposite.

Dim unnecessary lighting and reduce exposure to very bright screens close to bedtime. Keeping the bedroom dark, quiet and comfortably cool can also support normal sleep.

You do not need to eliminate blue light during the daytime. Daytime light is an important circadian signal. The goal is a strong contrast between bright days and dark nights.

Sleep Is Metabolic Medicine

Sleep isn't simply a period when nothing happens.

It is an active physiological state involving memory processing, hormonal regulation, nervous-system recovery, immune regulation and numerous restorative processes.

The source article discusses research showing that restricting otherwise healthy individuals to approximately five hours of sleep can impair glucose tolerance within only several days.

For most adults, a practical goal is approximately 7 to 9 hours of sleep per night, although individual requirements vary.

Consistency also matters. Going to bed and waking at approximately the same times each day helps reinforce the body's internal clock.

Meal Timing May Affect Your Biological Clock

Food is another powerful timing signal.

Dr. Satchidananda Panda and other researchers have investigated time-restricted eating—consuming the day's food within a consistent daily window rather than eating from shortly after awakening until immediately before bedtime.

The source article discusses research suggesting that organs benefit from a regular period without food and describes experimental work involving eating windows of approximately 8 to 12 hours.

However, much of the early mechanistic research was conducted in animals, and human responses vary. An 8-hour eating window should therefore not automatically be prescribed to everyone.

A simpler starting point for many adults is:

Finish eating approximately three hours before bedtime and maintain a consistent overnight period without food.

People who are pregnant, underweight, frail, have a history of eating disorders, take glucose-lowering medications, or have certain medical conditions should obtain individualized guidance before undertaking prolonged fasting.

Five Ways to Strengthen Your Circadian Rhythm

1. Wake at a Consistent Time

A reasonably consistent wake time provides the body with a dependable daily anchor.

2. Get Morning Daylight

Go outdoors after awakening when possible. Natural light provides a strong signal to the brain that daytime has begun.

3. Move During the Day

Walking, resistance exercise and other regular physical activity support metabolic health and can also strengthen the distinction between active daytime and restorative nighttime.

4. Stop Eating Several Hours Before Bed

Give digestion a chance to settle before sleep. Avoid turning late evening into another meal period.

5. Make Nighttime Dark

Dim lights as bedtime approaches, reduce unnecessary screen exposure and keep the bedroom as dark as reasonably possible.

Nutrition for Better Sleep and Circadian Health

A healthy circadian rhythm cannot compensate for a poor diet.

Build the diet primarily around whole, minimally processed foods.

Good choices include:

• Eggs, fish, poultry, lean meat, beans and lentils for protein
• Leafy greens and colorful vegetables
• Berries and other whole fruits
• Nuts and seeds
• Avocados
• Extra-virgin olive oil
• Fatty fish such as salmon, sardines and trout
• Fermented foods when tolerated

Limit excessive added sugar, sugary drinks, heavily processed foods and excessive alcohol.

Caffeine deserves particular attention. Its effects can persist for hours, so people having difficulty sleeping should consider reducing caffeine later in the day.

Alcohol can make someone feel sleepy initially while still interfering with normal sleep architecture later in the night.

Nutritional Supplements That May Be Considered

Supplements should supplement a healthy lifestyle, not compensate for irregular sleep, inadequate daylight, inactivity or a poor diet.

Depending upon the individual's diet, laboratory findings, medications and health history, nutritional support might include:

• Magnesium — particularly when dietary intake or magnesium status is inadequate.
• Vitamin D3 — when testing indicates deficiency or insufficiency.
• Omega-3 fatty acids — particularly when fatty-fish consumption is inadequate.
• B-complex vitamins — when dietary intake or individual nutritional requirements indicate a need.
• Vitamin B12 and folate — particularly when deficiency risk or laboratory testing indicates a problem.
• Glycine — sometimes used as part of nutritional sleep support.
• L-theanine — may be considered for selected individuals, particularly when difficulty relaxing contributes to poor sleep.
• Melatonin — may be appropriate for certain circadian-rhythm problems, but it is a hormone and should not automatically be treated as an everyday sleeping pill.

You may not need all—or any—of these supplements. Dr. Keefe can help determine which nutritional products may be appropriate for your individual needs.

For professional-grade supplements:

Access the Keefe Clinic Fullscript dispensary https://us.fullscript.com/welcome/jkeefe-dc

What About Melatonin?

Melatonin deserves special attention because it is frequently misunderstood.

Melatonin is primarily a darkness signal produced by the body. Levels normally rise in the evening as the biological night begins.

The source article emphasizes controlling evening light exposure as a fundamental way of supporting normal melatonin production.

Before automatically taking melatonin every night, consider the fundamentals:

Are you getting adequate daylight in the morning?

Are you using bright screens late at night?

Is your bedroom dark?

Are you maintaining a regular bedtime?

Are caffeine or alcohol interfering with sleep?

Sometimes correcting the environmental signals affecting the body's own circadian system is more appropriate than immediately adding another supplement.

The Keefe Clinic Perspective

One of the most overlooked principles of health is timing.

We frequently concentrate on what to eat, which supplements to take and how much exercise to perform while overlooking when we sleep, eat, exercise and expose ourselves to light.

The human body was designed around alternating periods of day and night, activity and rest, eating and fasting.

A good circadian-health program therefore begins with fundamentals: regular sleep, morning daylight, daytime activity, nutritious food, appropriate meal timing, stress management and a dark nighttime environment.

Nutritional supplementation can then be individualized according to the person's particular needs.

Bottom Line

Improving your circadian rhythm does not require an expensive program.

Start with five basic habits:

Get daylight in the morning. Move during the day. Eat primarily during the daytime. Dim the lights at night. Sleep on a consistent schedule.

Small changes performed consistently can provide stronger biological timing signals to virtually every system in the body.

The original article supplied for this review was published August 16, 2026 and notes that it is a reprint of an article originally published October 28, 2018.

Keefe Clinic

John H. Keefe III, D.C., P.C.

5640 South Memorial Drive, Suite A

Tulsa, Oklahoma 74145-9001

At 57th & Memorial

Phone: (918) 663-1111

Fax: (918) 663-2129

Email: docjohn@keefeclinic.com

Website: KeefeClinic.com