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Circadian Rhythms and Your Health

What time of night do you normally go to sleep?

Are you a self-proclaimed “midnight owl” who stays up until the wee hours working while others are sound asleep? Are you a fuddy-duddy, who as a rule gets to bed by 9:00 each evening?

I don’t remember who said it, but I once heard the phrase, “Nothing good ever happens after 10:00.”

Though there may be fun times to be had late into the evening on occasion, our ability to enjoy the evening well past sunset is a relatively new opportunity for humans. Just as many of the foods introduced to the human diet in the last few decades can wreak havoc on our health, never-ending hours of light may do the same.

Circadian Controls

An understanding of what triggers your circadian rhythm can help bring to life the importance of appropriate lifestyle choices. Triggers for circadian rhythm are called zeitgebers, which is German for “time-givers.” They are signals to the body that it is going through a specific part of the 24-hour cycle. The most studied zeitgeber is the light and dark continuum.

Unless you live in a cave, you’re exposed to natural light and dark cycles each day. Light travels from the eyes to the nuclei in the hypothalamus, called the suprachiasmatic nuclei (SCN). Exposure to natural light and dark cycles influences the way the body secretes hormones related to circadian rhythm.

Even without light, the SCN can maintain many aspects of the circadian rhythm, which tells us our bodies the time of day even if we don't have access to a clock.

That said, being exposed to artificial light on a schedule different than what our bodies are expecting can have negative effects. The light tells your body one thing while the SCN is telling it something else.

In addition to light/dark cycles, other zeigebers include food availability and unavailability or activity and inactivity. This means it is possible to disrupt the rhythm by eating when you should be fasting, or being active when you should be resting or sleeping.

Shift work can have the most disruptive effect on circadian rhythm, which explains why shift workers are more likely to have a dysfunctional metabolism. Those forced into short-term or long-term disruptions in normal lifestyle cycles should take extra steps to reduce other stressors in their lives.

Aside from exposure to light and dark, the cycle of feeding and fasting, and cycles of activity and inactivity, another well-studied zeitgeber is a hormone produced in the body called melatonin.

Melatonin and Circadian Rhythm

Melatonin is an internal zeitgeber, meaning the hormone acts to set the circadian rhythm on its own without direction from outside influences.

Melatonin is made from another hormone called serotonin. Melatonin production increases significantly about 9:00 p.m., but its production requires a decrease in light exposure. Extended exposure to light reduces normal melatonin production. Staring into a television screen late into the night reduces melatonin, which affects the ability to fall asleep or achieve deep, restorative sleep.

While melatonin supports a restful sleep, it does much more than that.

Research suggests that melatonin has the ability to regulate body fat levels, even without changing food intake, as well as the ability to reduce development of heart disease.

The other way of looking at these benefits is, disrupting melatonin production may cause unwanted body fat gains, acceleration of heart disease and other health complications. It may even play a role in degenerative diseases like Alzheimer’s.

During times of short-term stress, melatonin production increases, but under long-term stress, stores of melatonin can be used up, leaving individuals deficient in melatonin. In addition to its role in circadian rhythm, melatonin is also a powerful antioxidant, helping to rid the body of free radicals. Without enough melatonin, cancer-causing free radicals are more likely to cause cell damage.

Taking melatonin prior to intense cardiovascular exercise has been shown to reduce inflammation and oxidative stress. Though the use of melatonin may be helpful in reducing muscle damage, it can leave individuals drowsy post-workout. This may be useful for those who are forced to exercise late in the day and have trouble falling asleep once they get home. More research needs to be done in this area. 

Supplementation with melatonin can improve a variety of symptoms, including difficulty sleeping, but long-term lifestyle changes are still necessary. Melatonin supplementation can also be beneficial when adjusting to new time zones or even adjusting to daylight savings time. With the poor quality of sleep so many people are faced with today, it’s no wonder melatonin is one of the most popular nutritional supplements at Life Time.

Because supplementing with melatonin is safe, inexpensive and effective for most people, it is an easy way to reset normal sleep cycles for people who want to improve the quality and quantity of sleep. Doses range considerably, but a 3 mg dose is the most common.

Circadian Rhythms and Hormone Regulation

Clearly, disrupting normal circadian cycles can have a negative effect on an important hormone like melatonin, but understanding the natural flow of other hormones throughout a 24-hour cycle adds additional weight to the importance of maintaining a natural cycle. As mentioned above, a disrupted circadian rhythm has been shown to impact body fat regulation. One aspect could be the impact on body temperature. The production of heat is one of the ways the body helps to burn off extra energy, or calories. Under normal circumstances, body temperature varies throughout a 24-hour period. Though it has not been studied significantly, it’s possible this disruption could cause the body to burn less fuel as it is not maintaining temperature appropriately.

In the evening, under normal circumstances, the body becomes less sensitive to the hormone insulin, and less effective at managing loads of glucose. With normal circadian rhythm, growth hormone secretion increases at night, which helps the body utilize fat for fuel and makes it less effective at using carbohydrate, or glucose. Cortisol levels also fall in the evening and peak upon rising. As you can imagine, disrupting one’s circadian rhythm could affect the normal secretion of growth hormone and cortisol, both of which are critical to weight management, retention of lean body mass and many other effects.

Even the body’s ability to digest food and move it through the digestive tract follows a cyclical pattern. Research shows that meals consumed in the morning move through the digestive tract 50% faster than the same meal eaten in the evening. The implication of such a finding is that those who eat the majority of their food in the evening may not move food through the digestive tract fast enough for optimal health.

Something to Sleep on...

We tend to ignore the impact of long-term sleep deprivation. Some people even use a lack of sleep as a badge of honor. But make no mistake - ignoring normal sleep and wake patterns or shorting your body on sleep hours can have long-term ramifications. 

Over time these choices will disrupt the production of melatonin, an important sleep regulator and antioxidant. They will impair growth hormone production, which is critical to healthy aging and physical conditioning. Your choices will also interfere with normal cortisol production, which influences your body's ability to handle stress and eto maintain healthy metabolic functioning. And this isn't even an exhaustive list of the disruptions you'll set in motion....

Next time you consider staying up that extra hour to get a little more work done or to watch one more show, reflect on that choice and how it measures up against the value of your long-term health and current weight management priorities. 

Thanks for reading. Are you interested in learning more about how our schedules impact our health and metabolism? Speak with a registered dietitian today. 

Written by Tom Nikkola, Former Director of Life Time Weight Loss

Reference: Thomas Reilly, Greg Atkinson, Jim Waterhouse. 2010. Exercise, Circadian Rhythms, and Hormones. Michelle Warren, Naama Costantini. Sports Endocinology. Totowa, NJ. Humana Press.

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.

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Reader Comments (3)

My word, this article needs a proof reader. Information was useful but the spelling and grammar is awful.

June 24, 2012 | Unregistered CommenterMea

Do you have any suggestions for those of us who work nights and have to try to sleep during the day ?

June 24, 2012 | Unregistered CommenterUpallnight

I have worked nights my entire 27 year career (health care) and it took the first 6 months to one year to 'try' different schedules to see what worked best for me and my lifestyle (no husband/kids/family). To ensure that I sleep during the daylight hours when I'm on nightshift, I do two things that have consistently enhanced my ability to rest well:
1. Blackout shades: I have dark royal blue draw shades and it effectively makes it nearly night-time dark in my bedroom, which encourages your body to rest (dark= night= sleep)---also, I keep the room cool (celing and oscillating fans at work for this!)
2. I make every attempt to exercise when I get off shift in the morning---as little as a 3 mile walk with my dog, to a full cardio and weight training session, depending on my schedule. At first you may feel more wound up after the workout, but by the time you get home, shower, have a meal/snack and prep for bed, you should be wearing down.

Hope this helps. :-)

June 25, 2012 | Unregistered CommenterKaren C
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