What Is Chronobiology? [How Circadian Rhythms Affect Health]

Ever wondered why you’re a night owl but your best friend gets up at the crack of dawn? Circadian rhythms are behind this phenomenon. Each of us has our own built-in clock that is unique to us. Let’s learn more about a fascinating area of science called chronobiology, and how circadian rhythms are tied into our health.

What Is Chronobiology - Hands On A Clock

[kron-oh-bahy- ol– uh-jee] – is the science or study of the effect of time, especially rhythms, on living systems.

The 24-hour cycle we’re all familiar with is based on solar and lunar rhythms and the earth’s rotation. These biological rhythms are inherent in each of us, including plants and animals. Although other rhythms fall under the heading of Chronobiology, in this post I’ll be discussing circadian rhythms as their correlation to health has been researched the most extensively.

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What Is Chronobiology / Circadian Rhythms?

Circadian rhythms are internal clocks based on a 24-hour cycle that tell us when to wake up, when to eat, and when to sleep. They regulate many  processes in the body. The liver also plays a role in these rhythms via the proteins, AMPK and CK2, which are involved in metabolism, energy production, and cell division.

The hypothalamus is the head honcho when it comes to circadian rhythms. Glands are involved as well, including the pineal, thyroid, and adrenal glands. Their production of hormones are regulated by sleep/wake cycles.

Circadian clocks not only regulate hormone production and eating and sleeping patterns, but also brain wave activity, urine production, and cell regeneration. Cortisol and melatonin, hormones that oppose each other, are the most affected by circadian rhythms. When cortisol levels are high in the morning, melatonin levels are low.

As cortisol levels dip throughout the day, melatonin slowly begins to rise as evening approaches. Melatonin lowers body temperature in preparation for sleep, whereas cortisol raises blood sugar to stimulate alertness during the day. Cortisol is also a powerful anti-inflammatory hormone.

Circadian rhythms affect many physiological processes, including organ function. Although internal biological clocks are generated endogenously, they’re kind of like genetic-time clocks, and can be affected by external factors such as sunlight and temperature. An awareness of how circadian rhythms work is important because these rhythms can be influenced by lifestyle factors.

 Chronobiology And Health

Circadian rhythms not only affect sleep cycles, but also temperature regulation and digestion. If internal clocks are chronically out of sync, the propensity for disease increases. Any new mother can tell you how the lack of circadian rhythms in her newborn affects her health. We all know it takes awhile for babies to establish circadian rhythms, and it’s certainly a relief when they do.

Blind people tend to have problems with sleep since light is a predictive factor in establishing consistent rhythms. College students who pull all-nighters before an exam may get a nasty cold due to their immunity being impaired from disrupted circadian rhythms. It’s also not uncommon for travelers to come down with the flu following a vacation.

What Is Chronobiology - Sunrise

Have You Noticed These Rhythms?

Have you noticed you’re more productive in the morning? You have the energy to exercise or write or whatever else needs to be done.

You have the ability to plow through tasks with ease because your energy levels are high.

But what if you had to exercise at night or write a research paper? It’s highly likely you won’t be as productive.

Disclaimer: This article is strictly for informational purposes only and is not intended to be medical advice.

Afternoon Slump

We’re all familiar with the infamous slump that happens around 3:00 or 4:00 in the afternoon. Anticipate that this will happen and don’t engage in tasks that take a lot of mental prowess. This is called honoring your internal clock. Or take a relaxing stroll for ten minutes to reduce mental sluggishness.

When would be a more effective time to train for a marathon? In the morning or at night? I think I’ve made my point. Work with you internal clock instead of against it. Our circadian rhythms also ebb and flow on a weekly basis as most people can attest. Friday afternoon burnout is a real phenomenon.

If you’ve ever thought of calling a friend to chat at 6:00 p.m., you might want to re-evaluate. The chances of them being in the mood to talk will be slim if they’re just getting home from work, making dinner, have cranky kids, or just need some downtime to absorb the events of the day. However, this same friend may love to talk on their lunch break when their cortisol levels aren’t waning.

How Internal-Clock Disruption Can Affect Weight

Circadian rhythm disruptions can have an impact on weight. Consistent sleep/wake cycles and meal planning go a long way towards balancing fat burning hormones. Chronic sleep deprivation is also a contributing factor in insulin resistance, and eventually type 2 diabetes.

The “hunger hormones” leptin, ghrelin, and adiponectin fluctuate throughout the day, around meal times, and are influenced by sleep deprivation.

[Read More: How To Burn Fat Naturally By Activating These Hormones]

  • Leptin is made by fat cells and is called the satiety hormone because it decreases appetite.
  •  Ghrelin is produced in the stomach, and increases appetite and stimulates hunger. It increases on low-calorie diets.
  •  Adiponectin is also made in fat cells. The more your fat cells make, the leaner you’ll be because adiponectin burns fat and regulates blood sugar. The less adiponectin you make, the easier it is to gain weight.

You want these weight-regulating hormones working for because they have the important task of regulating metabolism and appetite. If they’re imbalanced, you won’t get the signal to stop eating when you’re full. Interestingly, cells are more insulin sensitive later in the day, allowing you to get away with eating more carbohydrates for dinner, and you’ll want your cortisol levels low in the evening to prepare your body for sleep.

What Is Chronobiology - Layla Sleep Banner

Factors That Interfere With Circadian Clocks

  • Flying at night
  • Traveling over time zones
  • Pulling all-nighters
  • Shift work
  • Not having regular meals
  • Daylight Saving Time

Many factors disrupt natural rhythms, especially if prolonged. Disrupted circadian rhythms are implicated in the development of metabolic syndrome, as well as type 2 diabetes. The stress hormone, cortisol, can also be negatively impacted, leading to problems with blood pressure and blood sugar.

Mood disorders worsen or arise if rhythms are disrupted for too long. Metabolism and immunity also take a hit. This is significant because a robust immune system is the body’s most powerful defense against cancer and chronic disease.

How To Reset Biological Rhythms

1. Develop consistent eating and sleeping schedules. Consistency will keep your internal clock ticking smoothly.

2. Bright light in the morning suppresses any residual melatonin and increases alertness.

3. Use yellow light bulbs in your lamps, instead of regular bulbs. They’re easier on the eyes and won’t interfere with melatonin production.

4. Use Nightshift if you have an iPhone. It shifts the natural blue light on your phone to a lovely yellow glow. Your ability to fall asleep won’t be hindered if you read books on your phone or watch movies in bed.

5. If your family has bright lights on – like mine does – in the evening, wear blue-blocker sunglasses a couple of hours before bed. The natural increase in melatonin as the evening progresses won’t be affected.

6. Light therapy in the morning can stimulate cortisol and increase alertness. It’s also good for alleviating seasonal affective disorder.

7. Taking a melatonin supplement at night can be helpful, especially when traveling, to combat jet lag.

8. Exercising too close to bedtime may interfere with cortisol levels, impairing the ability to fall asleep and stay asleep.

9. Sleeping on a latex pillow has really helped improve my quality of sleep. It stays cool and doesn’t lose its fluff like memory foam does. I take it with me when I travel to cut down on jet lag.

You likely won’t be aware of circadian rhythm swings if you’ve been getting enough sleep. However, if you’re chronically sleep deprived, you’ll be more likely to notice the natural ebb and flow of mental alertness and drowsiness.

Natural rhythms tend to fluctuate with the seasons and throughout the life cycle. As the sun sets earlier in the winter, people typically start getting drowsy earlier in the evening.  And we’ve all noticed how much sleep teenagers need.

What Is Chronobiology - FDN Banner

Key Points

Circadian rhythms are wired into all of us. Learning how they work and how they can be influenced by lifestyle, is an important factor in promoting good health and preventing disease. Being aware of how your individual circadian rhythms respond to external cues can provide pertinent information in identifying the routines that make you feel well.

How you noticed that circadian rhythms affect your health? Let me know in the comments:)


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(1) ScienceDirect: Chronobiology

(2) Scholarpedia: Chronobiology

(3) US National Library of Medicine National Institutes of Health: Chronobiology and mood disorders

(4) US National Library of Medicine National Institutes of Health: Methods in field chronobiology

(5) US National Library of Medicine National Institutes of Health: Chronobiology and Obesity: Interactions between Circadian Rhythms and Energy Regulation

(6) US National Library of Medicine National Institutes of Health: Chronobiology of the Immune System

(7) US National Library of Medicine National Institutes of Health: Chronobiology in mammalian health

(8) US National Library of Medicine National Institutes of Health: For Whom the Clock Ticks: Clinical Chronobiology for Infectious Diseases

2 thoughts on “What Is Chronobiology? [How Circadian Rhythms Affect Health]”

  1. Wow! As interesting as this is, this is the first time I have heard about this concept called chronobiology and how it affects our health. Logically, this makes sense to me, considering the fact that it simplifies the whole concept regarding our time and behavior patterns. Great article – I learned some new concepts. Thank you!

    • Thanks for reading my post on chronobiology. It’s quite a fascinating subject when you delve into it, and the impact it has on our physiology. It also sheds light on why some people are night owls and others are morning people. Circadian rhythms certainly do impact our health, and greatly affect our sleep/wake cycles. I appreciate your comment:)


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