Circadian Rhythm: Your 24 Hour Cycle


Here is a typical circadian rhythm with peak alertness at around 8 PM and 10 AM

The circadian rhythm acts as each person’s internal clock. It operates on a 24-hour cycle and affects various biological processes throughout the day, such as sleepiness, peak exercise potential, body temperature, and blood pressure. Many people find themselves particularly tired at around 2am to 4am, and drowsy in the hours after lunch, at around 2pm to 4pm. Many also experience periods of peak alertness, usually occurring between 9am to 11am and 7pm to 9pm. These cyclical periods of sleepiness and alertness are due to the circadian rhythm.

While the general timeline of the circadian rhythm is similar for most people, there can be significant variation in each individual’s circadian rhythms. It is possible to change your circadian rhythm through a few different mechanisms, like consistently changing your bedtime and waketime, exposure to sunlight, and temperature changes. When your bedtime and wake-up time is consistently later than average, then your circadian rhythm is shifted to later hours. In other words, instead of becoming tired at 10pm, a person with late sleep patterns might not become tired until 1 in the morning. Accordingly, they will be most alert at 1pm, instead of 10am.

To fall asleep earlier and wake up earlier than your current sleep pattern, it is necessary to change your circadian rhythm. It can be difficult to adjust sleep schedules because the circadian rhythm affects tiredness levels. If you are naturally tired in the early morning hours and fall asleep at 2am, it will be frustrating and likely futile to try to sleep at 10pm. Instead, try moving your bedtime back by 20-30 minutes gradually. As your circadian rhythm adjusts to your new bed- and wake-times, you will find yourself becoming sleepy at the time you desire. Similarly, slowly adjusting your waketime can be more effective than a sudden shift. When waketimes and bedtimes are consistent, your circadian rhythm will help you fall asleep and wake up more easily, as you will feel tired before bed and alert as you wake up.

Circadian components are affected by sleep schedules, but they are also affected by your environment, particularly, exposure to sunlight. When your body is exposed to sunshine, it causes a chemical reaction that makes your body feel more alert. By opening your blinds and turning on the lights as soon as you wake up, you will shake off morning grogginess more quickly than if you leave the blinds closed. Similarly, it often takes longer to fall asleep if you have just been exposed to bright light than if you were in a dimly lit room. By adjusting light exposure, you can help your body to feel alert or sleepy, depending on if you want to wake up or fall asleep. If you wake up before the sun rises, using a sunlamp to imitate the sun’s rays can be an effective tool to help combat sleepiness, without needing to use caffeine.

Napping during the day can help to alleviate the mid-day sleepiness that comes with the circadian rhythm. Short naps of 20-30 minutes during periods of tiredness can help keep you focused and alert throughout the day. Alternatively, drinking caffeine an hour before periods of tiredness can also help to keep you feeling fresh. By tracking your own periods of peak alertness and sleepiness, you can ascertain your own personal circadian rhythm. Knowing your unique energy rhythm means that you can better schedule your daily activities. If you always feel tired at 4pm, then you can schedule a run or a nap before this period to help reduce your feelings of tiredness. If you are at your most alert at 10am, then scheduling important meetings at this time can ensure that you will be alert and at you best.