Circadian Rhythm – What Is It and Is It Important?

It should be obvious that because we evolved on a planet with a 24-hour day that our biology is intrinsically linked to that day/night cycle. Our most basic patterns of behavior including our sleep cycle are keyed to the light and dark periods of a 24-hour day cycle. Scientists call this 24-hour cycle in plants and animals the circadian rhythm.

The daily circadian rhythm governs almost all our time-related biological functions including the sleep-wake cycle, metabolism, and mental health. Important biological mechanisms have been linked to the circadian rhythm including DNA repair that inhibits cancer and neurodegenerative disease prevention.

The Sleep-Wake Cycle

Your biological clock governs when you naturally feel sleepy and when you feel more alert. You may have noticed that you feel drowsy late at night and that you are more energetic in the late morning; that is because the circadian rhythm influences our energy levels and our sleep drive.

It should be noted that the circadian rhythm is heavily influenced by environmental factors, especially light. This is almost certainly related to our evolutionary development in which daytime offered opportunities to forage and hunt, while darkness inhibited such activities.

The circadian rhythm is controlled by the suprachiasmatic nucleus or SCN. The SCN is found in the hypothalamus and is sensitive to light. The SCN receives signals from the retinas that is initiated when light is visible. This then sets off a cascade of hormones that adjusts many bodily processes including appetite, body temperature, and sleep drive.

Among the hormonal changes that the SCN modulates is the rise in cortisol during the day—which boosts alertness—and melatonin after dark—which induces sleepiness. These hormonal pathways can be disrupted if we are exposed to light such as from a computer or TV.

Although the circadian rhythm does play an important role in the sleep-wake cycle, it is only one factor among many. Perhaps the most critical is the presence of fatigue toxins which indicate a lack of sleep. Another key factor is age—our circadian rhythms alter dramatically following infancy and adolescence, and when we enter old age.

A newborn will sleep up to 18 hours a day although this is broken up into shorter blocs. This will change at four to six months of age when the infant develops a circadian rhythm and will sleep for longer periods.

Teens will often experience a sleep phase delay in which their circadian rhythm will shift. That means that teens won’t feel sleepy until later at night and will often have greater difficulty arising in the morning.

Seniors tend to have a more erratic circadian rhythm. They tend to get sleepy earlier as well as rise earlier in the morning. They generally sleep less which can contribute to a cognitive decline.

The Importance of the Circadian Rhythm

Anyone who has experienced jet lag knows how uncomfortable a disrupted circadian rhythm can be. Jet lag, the common term for a disrupted sleep cycle due to travel across multiple time zones, produces fatigue, insomnia, and disorientation. Scientific evidence suggests that a dysfunctional circadian rhythm in animals can lead to serious health problems.

One study involving mice which the circadian rhythm was removed genetically were predisposed to obesity. This was, at least, partly due to an imbalance in glucose and lipid metabolism. This also contributed to a higher risk of diabetes.

Another rodent study found that hamsters that had a circadian rhythm genetic defect were at extremely high risk of developing renal and cardiovascular diseases. Subsequent studies of human shift workers showed that eating during a normal resting period often produced abnormal weight gain and altered insulin sensitivity. In addition to a higher risk of diabetes, shift workers were also predisposed to high blood pressure, cardio-metabolic syndromes, and inflammation.

There is also a suspected relationship between disruptions to the circadian rhythm and drug abuse. Not only can narcotics detrimentally affect the circadian rhythm, but a dysfunctional circadian rhythm can make you more prone to substance abuse. Unfortunately, in many cases, the disruption to the circadian rhythm may not abate even after discontinuation of drug use, which may be a contributing factor as to why drugs are so addictive.

Diagnosing and Treating Circadian Rhythm Disorders

It can be difficult to properly diagnose a disorder involving your circadian rhythm. If you suspect that your circadian rhythm is being disrupted, then you may need to consult with a sleep specialist.

Prior to seeing a specialist, your primary care physician may ask you about your sleep and work schedule. You may also be asked to keep a sleep diary for one or two weeks. Your doctor may also investigate if you are suffering from narcolepsy which may often present similarly to a sleep phase disorder.

In the course of diagnosing you, your physician may ask you to wear an actigraph which appears similar to a wristwatch and records your sleeping and waking activities. If necessary, you may be asked to participate in a sleep study which involves measuring various bodily functions while you are asleep; this may include brain activity, melatonin levels and body temperature.

Treating a circadian rhythm disorder will depend on the nature of the dysfunction and your ability to modify your lifestyle.

  • Behavior therapy—one of the first recommendations that your doctor is likely to make is to modify your lifestyle so that you adhere to your circadian rhythm. This may involve good sleep hygiene like following a strict bedtime and wake time as well as avoiding naps and caffeine.
  • Bright light therapy—exposure to bright lights at very specific times can advance or delay your sleep-wake cycle. This should help align your personal circadian rhythm with the natural day/night pattern and make it easier to attain sleep.
  • Medications—some drugs may be employed to adjust your circadian rhythm.  Commonly prescribed medications include melatonin which induces sleep and modafinil to promote wakefulness. The drug tasimelteon may be prescribed for patients suffering from non-24-hour sleep-wake disorder.

Article written by: Dr. Robert Moghim – CEO/Founder Colorado Pain Care

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