Circadian Rhythm Disorder Causes

Most of the time, a person's biological clock, or circadian rhythm, is in synchronization with the 24-hour day-night environment. In some individuals, however, the biological circadian rhythm of sleep and wakefulness is out of phase with the conventional or desired sleep-wake schedule. Some reasons for this breakdown may include the following:

• Sensitivity to zeitgebers ("time givers," such as light and other environmental cues): This sensitivity may be altered or disrupted, which can be demonstrated under certain conditions. Altered or disrupted sensitivity to zeitgebers is probably the most common cause of the circadian rhythm disorder of the sleep-wake cycle.

• Disrupted pacemaker function: A dysfunction may be present in the internal coupling mechanisms of biological pacemakers, for example, the coupling of the sleep-wake cycle with the temperature cycle.

• Environment: Light, higher noise levels, and elevated room temperature are not conducive to good sleep and are important variables to consider in both shift workers and night workers.

• Travel: The severity of jet lag is related to the direction of travel and is more frequently seen in individuals traveling in an eastward direction. The number of time zones crossed also has an effect on the severity of jet lag, with most individuals experiencing jet lag if they cross 3 or more time zones. The rate of adjustment is 1.5 hours per day after a westward flight and 1 hour per day after an eastward flight.

• Neurological disease: Alzheimer disease is one of the more common examples of neurological disease associated with a circadian rhythm disturbance; however, irregular sleep-wake cycles can also be seen in other neurodegenerative diseases. Sundowning, which is a common phenomenon in persons with Alzheimer disease, is characterized by sleep disruptions with awakenings and confusion.

• Shift work: Rapid shift changes and shift changes in the counterclockwise direction are most likely to cause symptoms of a circadian rhythm disorder.

• Lifestyle and social pressure to stay up late can exacerbate a circadian rhythm disorder.