Circadian Rhythm- A Biological Clock


Authors:
Veera Jaysaree Latha Bommu, MD
Neel Patel, MD
Lubna Mirza, MD (mentor)
Norman Endocrinology Associates

What is Circadian rhythm?

Circadian rhythm or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours

The term circadian comes from the Latin circa, meaning “around” (or “approximately”), and diēm, meaning “day” It may serve to imply that certain physiologic periods are close to 24 hours, if not exactly that length. Herein, “circadian” might be applied to all “24-hour” rhythms, whether or not their periods, individually or on the average, are different from 24 hours, longer or shorter, by a few minutes or hours.

To be called circadian, a biological rhythm must meet these three general criteria:

  1. The rhythm has an endogenous free-running period that lasts approximately 24 hours.
  2. The rhythms are entrainable.
  3. The rhythms exhibit temperature compensation.

How does it work?

Nearly every tissue and organ contain their own biological clocks. These are the result of certain proteins interacting with cells in the body, instructing them to be more active or to slow down.

One master clock in the body controls all these individual clocks. In humans, the master clock is a structure called the suprachiasmatic nucleus (SCN), which contains about 20,000 nerve cells and receives direct input from the eyes.

As the eyes perceive the bright light of day or the darkness of night, the SCN picks up on this information, telling the cells to act accordingly. Light keeps the circadian rhythm in sync with a 24-hour day.

In addition to reactions in the cells themselves, chemicals in the brain adjust in response to the cycles of the day.

These chemicals adjust a number of factors in the body, such as:

  • Hunger
  • Temperature
  • Arousal and awakeness
  • Mood

What are the uses of following Circadian Rhythm?

  • Healthy Circadian Rhythm can help in increased alertness, better sleep and supported health.

How does it affect our physical and mental health?

  • Circadian rhythm helps in maintain the health of almost all of our organs.
  • At what time we take our medicines for any kind of disease is very important as taking them at the wrong time of the day can give more severe adverse effect as if it is a poison.
  • At what time of the day we take flu shots, at what time we schedule a surgery for liver or heart are also important.
  • Even cancer patients were going through chemotherapy or radiation therapy it really matters whether they scheduled the chemo or radiation in the morning or late in the afternoon.
  • So, this new knowledge about circadian rhythm to start a new revolution in healthcare and healthy habits because the current idea of taking care of your health by counting calories and counting steps it just prehistoric.
  • Healthy Circadian Rhythm helps in maintaining metabolic functioning, body temperature, cardiovascular health, mood and cognitive functioning.

Effect of disrupted Circadian Rhythm for prolonged duration on various systems:

  • Effect on Hormones:
    Altered hypothalamo-pituitary (adrenal, thyroid, gonadal) axes.
    Can reduce the reproductive fitness.
  • Effect on Metabolism:
    – Altered lipid and glucose metabolism.
    – Altered Insulin sensitivity and glucose homeostasis.
    – Can result in obesity.
  • Effect on Cardiovascular health:
    – Disrupted Circadian Rhythm can affect lipid metabolism, hemostasis and increased inflammatory cytokines that can increase the risk of atherosclerosis.
    – Can increase the risk of high blood pressure, cardiomyopathy, myocardial infarction.
  • Effect on Neuro and Psychological health:
    –  Can cause headaches, loss of concentration, reduced cognition, and depression.
    – Can decrease sleep efficiency and leads to insomnia.
    – Can reduce hippocampal neurogenesis.
    – Increase the risk of oxidative stress and can result in dementia.
  • Effect on Children:
    – It can lead to autism as their brain is still developing.
  • Effect on cancer:
    – Can increase the risk of tumorigenesis.

What are the factors that can alter this cycle?

Changes in body and environmental changes cause our biological clock to go out of sync. Those are:

  • Eating large meals before bedtime.
  • Flying across time zones
  • Night shift work causes changes in the light-dark cycle.
  • Light from electronic devices at night can confuse our biological clocks.
  • Mutations or changes in certain genes.
  • Working in irregular shifts.
  • Pregnancy
  • Health conditions like Alzheimer’s disease and Parkinsons.

How are Biological Clocks related to jet lag?

When you travel through different time zones, your biological clock will be different from the local time. For example, if you fly east from Arizona to Florida, you “lose” 2 hours. When you wake up at 7:00 A.M. on the East Coast, your biological clock is still running on West Coast time, so you feel the way you might be at 5:00 A.M. Your biological clock will reset, but it will do so at a different rate. It usually takes a few days for your biological clock to align with a new time zone. Adjusting after “gaining” time may be slightly easier than after “losing” time because the brain adjusts differently in the two situations.

What can we do to maintain a healthy cycle?

  • It is a simple idea that we need more bright blue light during the day time and less light during night time is starting a new lighting revolution.
  • SCN also rely on external cues like light, food, noise and temperature.
  • Blue light from the electronic gadgets can alter the cycle since they send a lot of confusing signals and the brain thinks it’s not bedtime yet.
  • So, all the chemicals that’s actually not produced will go kind of go back and forth between insomnia and fogginess and if it continues for weeks or months, it would lead to insomnia and other health issues.
  • Having meals and snacks at the same time regularly is important for your gut health.

How can we fix the cycle disorders?

Conservative measures:

  • It is not only about dim down your smart phones and computer screen and turn orange during the night time.
  • Avoid eating round the clock.
  • Bright light therapy: spending at least some of the daytime in bright light.
  • Maintaining sleep hygiene.
  • Chronotherapy: Slowly adjusting the bedtime until it reaches your target time.
  • Lifestyle changes: having regular naps, being careful about bright light, caffeine, nicotine before bedtime.
  • We are biological beings. We are not our smart phones. We are not our computers. We need to be in touch with the rhythms of the nature.

Pharmacological treatment:

  • Over the counter Melatonin supplements.
  • Rozerem- Melatonin receptor stimulant.
  • Xanax- benzodiazepine in conjunction with behavioral therapy (not for long term use).
  • Non benzodiazepine hypnotics like Ambien, Sonata.
  • Belsomra- Orexin receptor antagonist.
  • Provigil- one week before shift work.

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