How Circadian Rhythms Act as the Body's Biological Clock

You have probably noticed the tendency to feel more energetic and alert during peak periods of the day and more lethargic and run-down at other times of the day. This is evidence of your circadian rhythms in action.

Your circadian rhythms are the cycle of physiological and biological processes that fluctuate on a roughly 24-hour timetable. All species have such a timing mechanism, or 'clock,' that controls periods of activity and inactivity.

While many people refer to circadian rhythms as a single process, there are actually a number of body clocks that oscillate throughout the day.

Woman sleeping in bed
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How Your Body 'Keeps Time'

A tiny cluster of approximately 20,000 neurons in the hypothalamus (a region of the brain) controls your body’s many circadian rhythms. Known as the suprachiasmatic nucleus (SCN), this master control center is responsible for acting as your body’s internal pacemaker.

While the exact mechanisms for how this process works are unclear, environmental cues are important. Bright light (often sunlight) controlling your daily sleep-wake schedule, is perhaps the most potent one.

As sunlight decreases at the close of the day, the visual system sends signals to the suprachiasmatic nucleus. Next, the SCN sends signals to the pineal gland to increase production of the hormone melatonin. This hormone increase helps reduce activity and makes you feel increasingly sleepy.

What Happens When There Is No Sunlight?

There has been a considerable amount of research on what happens to circadian rhythms when natural sunlight patterns are interrupted.

Clinical research has shown that individuals who are blind from birth frequently have difficulty with their sleep-wake cycle because of the complete lack of environmental light cues. Those who perform shift-work or travel frequently are also subject to having their natural circadian rhythms disrupted.

In some major studies of circadian rhythms, participants stayed in underground units for weeks or even months at a time. Deprived of all-natural light cues, the circadian rhythms of the participants began to shift toward a 28-hour schedule rather than the standard 24-hour pattern. Many of the body’s previously synchronized circadian rhythms shifted as well.

When exposed to environmental sunlight signals, many of the body's rhythms operate on a very similar schedule. When all-natural light cues are removed, these body clocks begin to operate on completely different schedules.

Key Points

  • Your circadian rhythms are tied to light cues.
  • Disrupting these patterns can lead to poor or difficult sleep.
  • Circadian rhythms also impact body temperature, pain sensitivity, mental alertness, physical strength, and senses.

Morning Larks and Night Owls

So-called 'morning people' prefer to get up with the sun and accomplish a great deal in the early hours of the day. 'Night people,' on the other hand, prefer to sleep in and consider themselves most productive during the evening hours. If this is pronounced, it may be a sleep disorder called 'delayed sleep-wake phase disorder.'

Still, night owls often find themselves forced to become early risers due to work, school, and caretaking obligations, and it turns out that might be a good thing for a number of reasons. Research has shown that people who get up earlier than their late-sleeping peers are not only happier, but healthier.

One study found that people who stayed up later tended to have worse cardiac functioning including heart rate and blood pressure. Not only that, but they also suffered from poorer sleep and were less likely to be physically active.

While individual differences in your biological clock may influence whether you are a morning lark or a night owl, there are a few things you can do to shift your internal clock and start greeting the day a bit earlier.

A few things you can try include:

  • Avoid loud noises and boisterous social situations in the late evening hours. Going to a late-night party or hanging out with roommates who are playing video games or watching movies can leave you feeling keyed-up and unable to sleep. Focus on giving yourself some time in the evening to unwind from the stresses of the day.
  • Follow a consistent sleep schedule. Start going to bed at the same time each night in order to wake up earlier without feeling sleep deprived. Avoid sleeping in on weekends more than 30 minutes compared to the time you wake up on the weekdays.
  • Minimize or eliminate nicotine, caffeine, and alcohol
  • Avoid daytime naps
  • Try avoiding bright lighting in the evening, including the blue-light emitted from screens like your cellphone, to see if this makes a difference.
  • Manage your time wisely during the day. Get stuff done earlier and avoid procrastination in order to prevent having to stay up late to finish things up.

It can take a while to establish a new waking/sleeping routine. Stick to it, however, and you may soon reap the benefits of being a morning person.

However, if these symptoms are not getting better after a few months, you should talk to your healthcare provider. There may be an underlying sleep disorder that may benefit from further treatment or another cause such as a medical or mental health disorder, substance use disorder, or medication side effect.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Kendra Cherry
Kendra Cherry, MS, is an author, educational consultant, and speaker focused on helping students learn about psychology.