Circadian Rhythms and Sleep

Insomnia can be manifested by circadian rhythm disorders, such as jet-lag or shiftwork. Insomnia can also contribute to a dynchronization of the circadian rhythm. Physiological and biological activities (body temperature, chemical/hormonal secretion, etc.) may become misalligned or suppressed because the insomniac is awake when he or she should be asleep. When assessing insomnia it is important to assess what effects it may have on the circadian rhythm, or conversely, what effects the circadian rhythm has on insomnia.

Human beings are a rhythmic species, experiencing cycles every 24 hours. These 24 hour cycles are known as circadian rhythms or more commonly known as one’s biological clock. In determining an individual’s circadian rhythm, a particular variable (i.e. body temperature, hormone secretions) must be measured repeatedly at different points of the day. When measured, systematic changes can be noted from one time of the day to another. These changes are consistent during a 24 hour period. For example, when one is asleep and body temperature is taken, it usually goes down during the night and early morning. This cycle repeats over a 24 hour period.

The purpose of this internal clock is to prepare the body and brain for sleep and active wakefulness at different times of the day. Moreover, the biological clock lowers body temperature, heart rate and blood pressure and controls the excretion of hormones like melatonin, which help induce sleep. The biological clock also protects our sleep by suppressing hunger and renal and bowel functions, permitting longer and more consolidated sleep with minimal disruptions. Combined, these factors produce a high quality of sleep.

When the biological clock becomes misalligned, due to jet-lag or shiftwork, sleep onset is difficult. A good sleep is important for it enables individuals to feel refreshed, energetic and vigilant, aiding with daily functioning. The inability to fall asleep at a “normal” time and obtain an adequate amount of sleep, can contribute to physical and psychological health difficulties, as well as negative safety and financial issues.

Dr. Alfonso Marino