The word Circadian comes from the Latin phrase circa diem, meaning about a day. Circadian rhythm is a function that repeats the same time every 24 hours, for example, night follows day each 24-hour cycle. In the body, the function may be physical, mental, or behavioral. A good example of a function in people is sleep, you get physically and mentally tired every 24 hours. Circadian functions in the body must be organized, automatic without outside assistance, and occur without an external clock. Think about hunger, every day we get hungry at about the same time of day. You don’t need the clock to tell you that you are hungry at about the same time each day, it just happens. Circadian rhythm usually follows external physical cues like light and dark, wet, and dry, or warm and cold. These universal cues put all living things on the same schedule and encourage cooperation. Light, temperature, actions, and social periods play a major role in establishing a circadian timing system. There is also a strong Individual component to circadian cycles. Factors such as sleep schedules, diet, stress, age, genes, medical conditions, and technology use all affect circadian rhythm.
A healthy circadian rhythm rolls with your genes. Each person has clock genes that determine optimal organization. Their function is to establish the clock in all cells, tissues, organs, and systems in the body. There are changes in the pattern of hormones between night and day, and summer and winter. This is important because it helps the body know how to anticipate and respond to the most basic changes in the world outside. There are many advantages to knowing that tomorrow will be a new day followed by night, or that after a hot summer, a cold season will follow. Likewise, we know that after we sleep, we feel more awake and ready to perform. A healthy circadian rhythm will have you working and playing at your best.
For a healthy circadian rhythm:
- Seek natural light exposure during the day.
- Follow a regular sleep-wake schedule.
- Follow a regular meal schedule.
- Get physical activity.
- Avoid large meals, alcohol, caffeine, and stimulants near bedtime.
- Avoid environmental challenges to sleep including noise, air pollution, and abrupt temperature changes.
Every day isn’t going to be perfect; illness and unexpected events happen. Medication, aging, and social interactions can also affect your clock. As much as possible, be aware of the timing of activities and circumstances. Manage your activities and circumstances to keep your circadian clock ticking.
It may be tempting to stay up late on the weekends or eat that ice cream late at night. While not recommended, occasional changes from your regular schedule are manageable. But frequent changes can throw off your circadian rhythm. This can negatively impact your health and well-being. It can result in a clock misalignment. And it may cause poor sleep quality and duration which leads to insomnia, sleepiness, bad mood, poor cognition, depression, and poor immunity.
Working with your body clock or circadian rhythm will promote good sleep. Good sleep leads to better health.
Miguel Meira Cruz PhD, DDS, MSc is head of the sleep unit of the Cardiovascular Center of the University of Lisbon, Faculty of Medicine, and is the Director of the European Sleep Center.