What Are Biological Rhythms?

Medically Reviewed by Carol DerSarkissian, MD on July 10, 2023
4 min read

Biological rhythm is a phrase often used interchangeably with circadian rhythm. These rhythms are a series of bodily functions regulated by your internal clock. They control cycles like sleep and wakefulness, body temperature, hormone secretion, and more. 

Your body maintains its biological rhythms through a variety of chemicals at the molecular level in response to your environment. Your light exposure, eating habits, and other environmental cues can maintain or disrupt your biological rhythms. Disrupting your biological rhythms can lead to serious health problems. 

Your biological rhythms are tied to an internal clock in your brain called the suprachiasmatic nucleus (SCN). It is located in your hypothalamus. This is the area of your brain that manages the autonomic nervous system and the pituitary gland. Your SCN sends signals throughout the day to regulate your body’s activity.

In cycles. Most biological rhythms work in roughly 24-hour cycles. Others, such as menstrual cycles, work over longer timeframes. Each type of biological rhythm has a certain name to show how long it lasts:

  • Diurnal (night and day)
  • Circadian (24 hours)
  • Ultradian (less than 24 hours)
  • Infradian/Circalunar (1 month)
  • Circannual (1 year)

Circadian and diurnal rhythms, which control functions like sleep, body temperature, and hormonal changes, are most affected by light. Sunlight tells your SCN what time it is and when to perform certain functions. Other factors that influence your internal clock are exercise, hormones, and any medications you might be taking.

Studies have shown the power of the internal clock by placing people in environments without the cues necessary for their circadian rhythms. Even without light cues, your SCN can maintain your body’s processes for a time with only slight deviations in its normal 24-hour rhythms.

Individual chronotypes. If your internal clock is so powerful, then why is it so hard to wake up in the morning? This is due to a circadian pattern called your chronotype. It is the biological tendency to deviate from a 24-hour cycle.

Night owls and early birds. Studies have also shown how the body’s circadian rhythms continue even in total darkness. Even without any light, people’s individual rhythms deviated only slightly from a strict 24-hour cycle. The population’s circadian cycles ranged on average between 23.5 hours and 24.6 hours. 

These deviations are due to people's personal chronotypes. Researchers believe them to be the cause of people being either an early bird or a night owl.

The main biological rhythm most people are concerned with is the diurnal sleep-wake cycle. It is the most obvious cycle you deal with on a regular basis. It has a powerful impact on your health.

During the day as you experience light cues, your SNC sends signals of alertness to tell your body it’s time to be awake. As the sun sets, your SNC signals for the production of melatonin, a sleep hormone. Afterward, it continues signaling to your body to stay asleep. 

Other than sleep, your biological rhythms influence important functions such as:

  • Metabolism
  • Heart rate
  • Blood pressure
  • Body temperature
  • Hormone levels
  • Urine production

Your biological rhythms are also tied to the regulation of blood sugar and cholesterol, risks associated with mental health that lead to depression, bipolar disorder, and neurodegenerative diseases. Biological rhythms also influence your immune system, DNA repair processes, and cancer treatment effectiveness.

Your biological rhythms can be disrupted by short-term and long-term causes. Sometimes these disruptions are caused by natural changes to your biological rhythms as you age. Other times, it can be due to alterations in your environment and activities.

Jet lag disorder. Jet lag is the most common disruption of your biological rhythms. This occurs when someone travels across several time zones, such as flying between two distant countries. The rapid change between time zones confuses your internal clock. The length of time jet lag's symptoms last will vary depending on the number of time zones crossed. Some of them are:

  • Insomnia
  • General sleepiness or fatigue
  • Indigestion
  • Irritability
  • Lack of focus

Shift work disorder. Work is another major disruption. Jobs that require working in shifts (as opposed to a 9 a.m. to 5 p.m. job) often limit your exposure to typical daylight cycles. Nighttime shifts are major culprits for this type of disruption. They typically force you to sleep during the daytime, conflicting with your natural inclinations.

Delayed sleep phase disorder (DSP). This type of disruption is usually a problem for night owls. People who have DSP tend to get tired far later than the average person and sleep in later than normal. DSP is mostly seen in teens and young adults and can make waking up for school or work more difficult.

Irregular sleep-wake rhythm disorder. This is a rare disorder that makes it so a person doesn’t have a consistent sleep pattern. It could be characterized by constantly changing bedtimes or regularly napping throughout the day. Irregular sleep-wake rhythm disorder is commonly associated with brain conditions such as dementia or brain injuries.

To keep your biological rhythms in time and consistent, practice the following habits:

  • Soak in some sunlight early in your day to reinforce your biological cues.
  • Go to bed and wake up at the same time every day.
  • Exercise during the day to make it easier to sleep at night and to reinforce your waking hours. 
  • Avoid caffeine after 12 p.m. to make sure you can fall asleep.
  • Avoid artificial light from electronic devices before bed.
  • Don’t take long naps and don’t nap too close to bedtime.