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What are Circadian Rhythms?

Circadian Rhythms are our body’s natural cycles that control appetite, energy, mood, sleep and libido. When our body is out of sync with nature, we suffer from a Circadian Rhythm Disorder. Almost all of us, at some time during a year fall out of balance and suffer from sleep, mood or anxiety disorders. Fortunately, after decades of research, science has found the way to create circadian balance.


Nature’s Rhythms

Much of nature is made up of rhythms or cycles. Common rhythms include the four seasons and the twenty-four hour rotation of the earth. Like nature, our bodies have rhythms. Some of the rhythms of body and mind are tied to nature. When working properly, our bodies respond to nature’s cues to create their ideal rhythms. For example, when functioning properly, the human circadian rhythm will respond to the morning light of a new day. This light will cue the body to produce cortisol, serotonin, and other hormones and neurotransmitters that get a person awake and going and cause blood pressure to increase and body temperature to rise.

At sunset, the body receives another of nature’s cues and responds to dusk and ultimately the night’s darkness. As the sun goes down the body will produce and secrete the hormone melatonin, and blood pressure will drop as the body prepares for and eventually falls off to sleep.

In reality circadian rhythms control the timing, quantity and quality of the hormones and neurotransmitters the body produces and eventually secretes. Hormones and neurotransmitters are the elements that determine how we feel, our sleep patterns, our appetite, our sex drive and other sleep and mood-related issues. When functioning properly, our circadian rhythms create circadian balance. When out of balance, quantity, quality and timing of hormone and neurotransmitter secretion suffer and our bodies suffer from a circadian rhythm disorder (CRD).

Why Circadian Rhythms are Becoming a Greater Issue

The Master Clock or Body Clock

Significant progress is being made in the field of chronobiology, the formal name for the medical science that studies circadian rhythms. Researchers have discovered that the human body is orchestrated by internal biological clocks marching to several internal rhythms that pace themselves hourly, daily, monthly, seasonally and even yearly.

Central to the timekeeping mechanism of the body and mind are Suprachaismatic nuclei or SCN. The SCN is the master clock – the circadian rhythm that controls all other rhythms of the body. The SCN is actually two clusters of 50,000 neurons, one on each side of the brain. The SCN sits inside the hypothalamus region of the brain and works with several time keeping genes. Together, the SCN and the timekeeping genes make up the central clock which governs many aspects of physiology and behavior because they orchestrate the daily rhythms and cycles that control the ebb and flow of hormones, chemicals and neurotransmitters that determine wake, sleep, appetite, sex and other key aspects of our lives. It is vitally important to understand the SCN and to how to care for it.

Circadian science

The study of circadian rhythms dates back to the 19 th century. However, significant studies and observations began in earnest in the 1960’s. One early pioneer was Curt Paul Richter, a professor of psychobiology at Johns Hopkins Medical School whose innovative concepts are the foundation for established concepts and methods for studying circadian rhythms in humans.

The word circadian is Latin in origin from the word circa meaning “about” or “approximately” and dian meaning “day”. The term circadian was coined when Franz Halberg, a scientist at the University of Minnesota, published a paper in 1959 showing blood count varied according to a strict rhythm that was about a day. In fact, Halberg discovered that the rhythms actually went somewhat longer than a twenty-four hour day.

The field of chronobiology, the medical discipline that studies circadian rhythms, has since revealed that the body undergoes more than just blood count variations. In fact, the body makes significant changes throughout a day.

Human’s Free-running rhythm
Beginning in 1980, several studies were conducted to learn more about the human circadian rhythm. These studies included placing people in an isolated environment without any external cues or clues as to what time it was. These studies conclude that, if left alone, healthy humans undergo changes based on an internal clock that is longer than twenty-four hours. These changes in biological rhythms can be measured in physical strength, aerobic capacity, body temperature, blood pressure, mental alertness, production and secretion of neurotransmitters & hormones, and many other body functions.

No one knows for sure why the cycle is more than twenty-four hours as opposed to precisely twenty-four hours, nevertheless, herein lies part of the problem. If the internal circadian clock of an individual is “free-running”, (a state in which the body is not receiving external signals or cues) it is only a matter of time before lifestyle realities clash with free-running circadian time. This clash means hormone and neurotransmitter secretion becomes confused and will create problems for their health.

Zeitgebers: The Body’s Way of Synchronizing

In order for to reconcile the difference between natures exact twenty-four hour cycle and the internal circadian rhythms we free-run on, nature has given us “zeitgebers”, a German word that means “time givers”. As modern lifestyles demand more flexibility in schedules, man has lost touch with its most valuable zeitgerber, which is the sun. Modern lifestyles, work schedules, and indoor living has altered the amount of sunlight we receive as well as how we set our schedules.

It used to be that people generally woke up at dawn, worked and spent much of their day outside or near a window, and at nighttime they read by low levels of light until retiring to bed. For better or worse, we don’t follow that pattern any longer.

Social zeitgebers are important in organizing the human day. The alarm clock is an important social cue. It wakes us up and helps us to get on our schedule. Other social zeitgebers include daily activities such as eating meals together with a family, watching television, reading the mail or other regimented type of activities that are habitual in nature.

Circadian Rhythm Disorders

Out of Synch: what is circadian rhythm disorder?

A circadian rhythm disorder means your body is producing hormones, chemicals and neurotransmitters in the wrong amounts and/or at the wrong time of the day. Circadian rhythms stimulate the timing and production of countless hormones and chemicals that affect your sleep and mood. Circadian rhythms permeate practically every aspect of our lives because they so heavily influence the chemicals that determine our mood and sleep.

Nature, through its twenty-four hour cycle of day and night, has provided us with a template or a pattern that anticipates what we need to be healthy. Nature has obviously anticipated our needs and when properly synchronized, our bodies respond to nature’s external cues.

The timing of psychological, behavioral, physiological, and hormonal rhythms with respect to natures external day-night cycle, clearly imply that temporal order is essential for optimal health. If this is true, then temporal disorder is a potential recipe for health and wellness disaster as indicated by a host of clinical and non-clinical studies. Clearly, many forms of mood and sleep problems can be traced to a circadian rhythm disturbance.

Because the circadian rhythm influences so much of how a person feels or sleeps, if a person desires optimal health, they need to manage their circadian rhythm. If a circadian rhythm is out of balance, other health aspects will be impacted and out of balance as well.

The Results of Circadian Rhythm Disorder

New research regarding the human circadian rhythm and its affect on your body is surfacing on a weekly basis. In fact, research studies are being done to determine the impact of the circadian rhythm on hypertension, cancer and a host of other diseases. Over the last couple of decades there has been significant research and clinical studies on circadian rhythm as it relates to mood and sleep disorders.

Because circadian rhythms control the release and timing of hormones, circadian rhythm disorder underlies many mood and sleep disorders. Following are some examples of how circadian rhythm disorder affects specific kinds of mood and sleep disorders.

Depressive Disorders

Clinical Depression

Researchers report that depression is closely tied to circadian rhythm disorders because almost all depression sufferers have sleep problems and feel worse at a particular time of day as well as in the winter. When treated with bright light, these problems improved significantly. Because bright light quickly corrects the circadian imbalance in depression, patients respond to light within a week verses months with antidepressant medications.

The fact that depression is circadian related is further evidenced through a new treatment known as wake therapy. Researchers believe that depression sufferers have unresponsive body clocks. Wake therapy awakens the patient several hours early, which blocks any feedback signals to the body clock when it is most active. This effect ‘reboots’ the body clock, causing it to revert to an active day cycle. With wake therapy, symptoms of depression disappear almost immediately. Wake therapy is only necessary for the first night if used with bright light each successive morning.

This revelation on circadian rhythms and depression has led researchers to conclude, "These common experiences suggest that disruptions in biological clocks may be both cause and consequence of disturbed moods."-- Michael Smolensky, The Body Clock Guide to Better Health

Seasonal Affective Disorder (SAD)

No other mood disorder is more closely associated with circadian rhythm disorder than Seasonal Affective Disorder or SAD. During the dark fall and winter months, the brain’s control center, the Suprachaismatic Nucleus (SCN) or body clock doesn’t receive the proper stimulus of light. The SCN needs bright light signals to reset itself each day. When it doesn't receive this signal, it malfunctions and produces the wrong hormones at the wrong time of day.

Research also shows that without sunlight, the brain doesn't produce enough serotonin, resulting in the symptoms of depression . The darker days also signal the brain to overproduce the hibernation hormone, melatonin. The symptoms diminish as the days get longer, although many SAD sufferers note brief (1-2 week) periods of SAD like symptoms in the summer.

Bipolar Disorder

Bipolar Disorder is different than major depression in that it is marked by episodes of euphoria or mania. These episodes can last for hours, days or even months. In almost all cases of Bipolar Disorder, depressive and manic episodes are seasonal. In the Fall and Winter, bipolar sufferers enter a depressive phase, and require increased intervention. Bipolar sufferers also suffer from sleep problems and feel worse at a particular time of day. Because these symptoms reflect a circadian rhythm disorder, doctors have found success by treating bipolar disorders with bright light.

Premenstrual Syndrome (PMS)

Premenstrual Syndrome (PMS) is a combination of physical discomforts and emotional symptoms that happen during the latter half of the menstrual cycle and usually let up during the first few days of menstruation. PMS is marked by low levels of progesterone and serotonin hormones. Researchers believe these hormones may deplete too quickly, and not allow enough time for the body to adjust. During this period, women’s body clocks also speed up causing melatonin to be released prematurely and the supply of serotonin to be cut off. This may account for the increased pain, irritability and sleep problems.

Chronic illnesses are also at their worst during PMS. Asthma, depression, diabetes, fibromyalgia, hot flashes, migraines, acne, rheumatoid arthritis, are all affected by this change in hormone levels.

Bright Light helps PMS

Women’s health researchers discovered that PMS is tied to circadian rhythms. Apparently, the body clock begins to cycle too quickly during the second half of the menstrual cycle, and may be a reason why these reproductive hormones deplete too quickly. Light is known to produce serotonin, the mood hormone lacking in PMS sufferers. Evening light is also the most effective way to slow the body clock down to a normal rhythm. When researchers used light to slow the body clock back down, symptoms of PMS also dissipated. The discovery that light reduces menstrual problems as well as regulates cycles, is encouraging, particularly for women who are seeking natural alternatives:

“This apparently powerful – yet simple and seemingly safe—methodology should lead to exciting progress in our understanding of human reproductive endocrinology.” – Daniel Kripke MD, Head of Chronobiology Research, UCSD.

Premenstrual Dysphoric Disorder (PMDD)

PMDD is a short-term depression, which occurs during the latter part of the menstrual cycle. PMDD is usually associated with more severe symptoms of PMS and interferes with the ability to interact socially. Approximately 5-10% of PMS sufferers also have PMDD. The difference between PMMD and other disorders is that its symptoms generally appear the week prior to menstruation.

There is a strong connection between PMDD and low serotonin. Serotonin acts as a calming hormone. When serotonin levels are restored, many of the more destructive symptoms of PMDD disappear, such as pain, anxiety, irritability, anger and food cravings.

The discovery that light regulates serotonin and melatonin is significant, because these hormones are linked to PMDD. For example, studies show that women suffering from PMS and PMMD not only have low levels of serotonin, but that their body clocks are running too fast. This releases the withdrawal hormone, melatonin, too early, which depletes serotonin reserves and causes sleep problems. Using this special light in the evening will slow the body clock back down and balance natural serotonin levels.

Since light is known to produce serotonin as well as reset the body clock, researchers at UCSD have had success using Apollo’s Britewave technology in treating women with PMS and PMDD. Adding light a week before PMS or PMDD occurred, cut symptoms by at least 50%. This was more effective than drugs alone, but relief was even greater when light was used in conjunction with medication, especially for women with severe symptoms. Many women reported complete relief from light alone.

Prenatal and Postpartum Depression

Prenatal and postpartum depressions are depressive disorders that occur during or within a year after pregnancy, afflicting 10% of all women. Prenatal and postpartum depressions are among the most serious mood disorders for women because they impact the health of the fetus and newborn. An expectant mother will not take as good care of herself, which may harm the fetus. Studies also show that depressed mothers don’t care for their babies as well as other mothers. They talk less, show less affection and don’t’ respond as well. As a result, their babies have more problems socially; they withdraw, and are less animated than other babies. Commenting on the long-term consequences,

“Children of depressed mothers are at increased risk for anxiety disorders in childhood, major depression in adolescence, and alcohol dependence in early adulthood. Furthermore, depressed offspring of depressed parents have a longer duration of episodes, more impairment, more medical problems and receive less mental health treatment. In addition to having more serious and recurrent depression, they are more socially and vocationally impaired. Thus, to reverse these adverse consequences of maternal depression, treatments need to be instituted early in the course of the illness.”

Why expectant and new mothers become depressed

Pregnancy and delivery causes hormone levels in some women to be too low. During pregnancy, the body clock releases hormones that increase the body’s ability to deal with the added stress of having a baby. These hormones take their toll though, by depleting reserves of serotonin, the hormone associated with wellness and mood. During the third trimester and just after birth, serotonin levels are as low as those found in people with major depression. This is why over 70% of new mothers experience the ‘blues,’ and 10% suffer from depressive illnesses.

Pregnancy and postpartum depressions affect the body clock
Researchers have also noted a strong connection between circadian rhythms and pregnancy related depressions. Symptoms are generally worse in the morning time, and the sleep problems are a result of disrupted circadian rhythms. Since light is known to produce serotonin as well as reset the body clock, researchers at Yale and UCSD have had success using Apollo’s BRITEWAVE™ technology in treating women with pregnancy related depressions. In this case, the specialized light is used in the morning time. News that morning bright light is helpful is important because anti-depressant medication is undesirable during pregnancy and nursing.

Sleep Disorders


Because the circadian rhythm controls the sleep/wake cycle, circadian rhythm disorder often results in insomnia. If there is a pattern to the sleep disturbance, i.e., one consistently wakes up or falls asleep at the wrong time, or if he/she cannot get to sleep at certain times, it is most likely that his/her circadian rhythm is malfunctioning.

The American Academy of Sleep Medicine (AASM) estimates that 25% of all sleep problems are directly related to circadian sleep disorders and several other sleep problems are either caused by or contribute to circadian rhythm disorders. These sleep disorders include late night and early morning, insomnia, interrupted sleep patterns, free-cycling sleep disturbances and irregular sleep disorders. (For specific information on all circadian related sleep disorders, visit the sleep section on this webpage.) The two most common sleep problems—Late night and early morning insomnia are discussed below.

Late Night Insomnia

The majority of people with sleep problems experience difficulty being able to fall asleep. They may only experience a few hours of sleep each night, and feel worse in the morning time. In this case, the body clock is running slower than a normal circadian rhythm (24 hour period). The clinical term for late night insomnia is Delayed Circadian Rhythm Disorder or DCR. DCR sufferers’ body clock doesn't 'wake up' until later in the morning or day. They have difficulty getting started in the morning, may feel a bit groggy or down during part of the day, and may experience a second wind later in the evening. Those with DCR are often referred to as night owls, and find it easier to stay up late at night.

With DCR, the daily cycle, or circadian rhythm is running slow, and the pineal gland releases the nighttime hormone melatonin too late, causing sleep to occur later. In the morning, the body clock is still producing the nighttime hormones. This is why it may take several hours to feel active and energetic. Because DCR sufferers don't receive the proper amount of sleep, energy, alertness and ability to function may also be diminished.

Because DCR is the result of a slower circadian rhythm, bright morning light is the most successful means to speed the body clock up and restore circadian rhythms to their normal function. Because DCR disorders vary with individuals, the treatment schedule needs to be adapted accordingly. Apollo provides an effective assessment tool on its website for determining the proper treatment schedule and guidelines.

Early Morning Insomnia

As people age, they tend to have difficulty staying asleep, and usually awaken hours before dawn. Those with early morning insomnia generally tire easily in the afternoon or evening and have little difficulty falling asleep. The clinical term for this disorder is Advanced Circadian Rhythm Disorder or ACR. ACR happens when the body clock is running faster than a normal 24-hour period. Because the body clock is running too fast, ACR sufferers tend to run out of energy before the 'day' or 24 hour period is through. ACR also tends to compress the sleep portion of the daily cycle, causing ACR sufferers to often sleep less than 8 hours per night.

Because the circadian rhythm is running fast, the pineal gland releases the nighttime hormone melatonin prematurely, causing one to feel tired earlier in the evening. Since melatonin is released prematurely, the body clock can't sustain a complete sleep cycle, causing early insomnia.

Bright evening light has been shown to be the most effective treatment for ACR. Evening light slows the body clock down to a normal rhythm. This delays the onset of melatonin and sleep, allowing the person to sleep longer and have more energy in the late afternoon and evening.

CRD's contribute to other sleep disorders

Circadian Rhythm Disorders keep our bodies from enjoying a complete or rejuvenating sleep. Because CRD's disrupt the sleep pattern, they may contribute to narcolepsy, sleep apnea, snoring, etc. Most people find these symptoms diminish when their circadian rhythms are working properly

Other Disorders that show a circadian Pattern

Jet Lag

Jetlag is the result of one’s body clock being out of synch with a new time zone. The symptoms of jet lag are similar to depression, and will persist until the body clock can respond to the new time. Without intervention, this process takes one to two weeks, depending on the distance traveled. Jet lag is easily avoided by using timed bright light to speed up the body clock’s adaptation to the new time.

Shift Work

Shift work almost always causes a circadian rhythm disruption, where a person's internal body clock is at odds with the shift schedule. Shift work problems are well documented and range from perfomance issues to accidents and other health problems. Recent evidence shows that shift work may contribute to cancer because working at night in well lit enviornments suppresses melatonin, which acts as a powerful anti oxident. Additionally, proper circadian signaling causes cells to die, and shift workers may not be receiving these needed signals. As a result, mutated or deformed cells continue to grow when they otherwise would be destroyed.

Shift workers can easily adapt their body clocks to work within the shift schedule's requirements by using a light therapy protocol. Using this protocol will increase work performance, improve sleep and off-shift scheduling problems, as well as decrease health and cancer related risks.

Chronic Fatigue Syndrome

The Centers for Disease Control and Prevention (CDC) has documented that a circadian pattern exists in Chronic Fatigue Syndrome (CFS). Pain, fatigue, mood, social activity, energy, sleep and weight worsened significantly in the Winter. In addition, about half of CFS sufferers also have major depression in the Winter. Because circadian rhythms affect CFS, researchers have found success treating with light therapy, and have commented that, “Light therapy may provide patients with CFS an effective treatment alternative or adjunct to antidepressant drugs.”

What causes circadian rhythm disorder?

Unfortunately, modern living has dramatically altered nature’s cues. We have developed lifestyle patterns, shelter, conveniences, and modes of travel that dramatically influence the cues that drive other mammals. A modern day does not start at the crack of dawn or end at 8pm.

In a modern day, we get up when the alarm clock tells us too, work indoors, often in inner cities or interior offices where there is very little sunlight or the intensity is ineffective in resetting our circadian clocks. After-work time is spent indoors at social gatherings or in front of the television or computer often late into the night. We go to bed late, usually far after we are tired, and as a result, we are dependant on an alarm clock to get us up in the morning. Unfortunately, we wake up to man made cues and our circadian rhythm has not cued our body to secrete the proper hormones and neurotransmitters resulting in an imbalance.

Unfortunately, very few of us get the amount of daylight needed. In the modern world, we live, work, and play primarily indoors. In fact, one study conducted in San Diego, one of the sunniest and ideal climates in the world found that people there received less than one hour of sunlight each day. The light they received was primarily to and from work while sitting in a car.

When our bodies are out of balance nothing seems to feel right. This is because the hormones, chemicals and neurotransmitters that determine how we feel, sleep and eat are out of sync. The result is a Circadian Rhythm Disorder.

Creating circadian balance

Circadian Balance is the state we enjoy when our bodies sleep well, eat right, have lots of energy and feel great; when in balance we are at our best.

Circadian Light Therapy Resets and Stabilizes the Circadian Clock

Light is the most effective way to synchronize the body with the twenty-four hour day. In the early 1980’s two groundbreaking studies were conducted; one study was conducted at the Albert Einstein College of Medicine in New York and another at the National Institute of Mental Health. Both of these studies concluded that specific wavelengths, intensities and color spectrum of light, (not available in ordinary room lighting) could reset the circadian clock and create circadian balance. Since that time, numerous studies have been conducted to understand how and why light therapy works.

Light, when created in a circadian correct intensity, wavelength and color spectrum, has been clinically proven to reset the circadian clock. In addition to resetting the clock, light has a direct and positive impact by increasing brain serotonin levels. At the same time circadian light therapy has a depressing affect on daytime melatonin. Excessive daytime melatonin has also been linked to depression and sleep disorders.

A key point of the SCN is its location in the human body. Because the SCN sits in the hypothalmus, it is connected to the optic nerve. When the eye is exposed to circadian light the SCN receives this signal and utilizes it as it regulates the circadian cycle. Unfortunately, most people no longer get enough daylight to receive the cues that nature intended and as a result there are millions of people suffering from some form of circadian rhythm disorder.

If you feel you may have a circadian rhythm disorder, you can take a free Circadian Rhythm assessment here

See appendix I “Sizing the Market”

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Smolensky, M., L. Lamberg. The Body Clock Guide to Better Health. Henry Holt and Company, LLC.

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