How Circadian Rhythms Act as the Body's Biological Clock

All species have a timing mechanism, or 'clock,' that controls periods of activity and inactivity. These clocks are known as circadian rhythms and refer to the cycle of physiological and biological processes that fluctuate on a roughly 24-hour timetable. You have probably noticed these tendencies yourself, feeling more energetic and alert during peak periods of the day and more lethargic and run-down at other times of the day.

While many people refer to circadian rhythms as a single process, there are actually a number of body clocks that oscillate throughout the day. For example, mental alertness tends to peak twice in a day at 9 AM and 9 PM, while physical strength tends to crest at 11 AM and 7 PM.

Woman sleeping in bed
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How Your Body "Keeps Time"

A tiny cluster of approximately 20,000 neurons in the hypothalamus 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. Sunlight is perhaps the most apparent, controlling our daily sleep-wake schedule.

So how does sunlight affect your circadian rhythms? As the 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 the production of the hormone melatonin. This hormone increase helps reduced 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 these participants began to shift toward a 25-hour schedule rather than the standard 24-hour pattern. Additionally, 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.

A Few Key Points to Remember

  • Your circadian rhythms are tied to sunlight cues.
  • Disrupting these patterns can lead to poor or difficult sleep.
  • Without light signals, people tend to operate on a 25-hour schedule.
  • Circadian rhythms also impact body temperature, pain sensitivity, mental alertness, physical strength, and senses.

Morning Lark or Night Owl

Would you describe yourself as more of a morning person or a night person? 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 the most productive during the evening hours.

Even night owls often find themselves forced to become early risers due to work and school obligations, and it turns out that might be a good thing for a number of reasons. Research has shown that morning people are not only happier than their late-sleeping peers, they're also healthier.

One recent study found that people who prefer to stay up later tend 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.

The research also found that both morning and evening types are better capable of handling stress in the early hours of the day. So the next time you're facing an anxiety-provoking work or school project, try working in it early in the morning rather than in the afternoon. By putting things off until later in the day, you're actually creating more stress for yourself which may ultimately affect the quality of your sleep.

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:

  • 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 projects.
  • 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.

According to sleep experts, it may take up to a month to establish a new waking/sleeping routine. Stick to it, however, and you may soon reap the benefits of being a morning person.

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  • Whitbourne, S. K. (2012). Morning Person or Evening Person? How Your Body’s Clock Affects Your Life, Psychology Today.