To say that humans are a creature of habit is not just a cliché, it’s a scientifically proven statement. All mammals, including humans, are subject to circadian rhythms, which are regular changes in mental and physical characteristics that occur in the course of a day.
Circadian rhythms are important in determining sleeping and eating patterns. There are clear patterns of core body temperature, brain wave activity, hormone (melatonin) production, cell regeneration and other biological activities linked to this daily cycle, which are often triggered by light exposure or other routine external factors such as an alarm clock.
Every individual has his or her own rhythm. There are those people who naturally prefer to sleep and wake early--called “larks” or “morning people”--and then there are those who prefer to sleep and wake at late times called “owls.” These sleep patterns are still considered normal and healthy as long as the individual:
Can wake in time for what they need to do in the morning, and fall asleep at night in time to get enough sleep before getting up again;
Can sleep and wake up at the same time every day, if they want to;
Can, within a few days of starting a new sleep/wake routine, naturally adjust their rhythm without decreasing the amount of sleep they get.
People who are unable to sleep and wake at the times required for normal work, school or other social needs could be suffering from a family of sleep disorders called circadian rhythm sleep disorders. Generally these people are able to get enough sleep, but not at hours that support a normal 8 a.m. to 5 p.m. job. In this case, the disorder may be alleviated by working a job with adjusted hours such as a swing shift.
Although shift work may be suitable for some people, it can instigate a circadian rhythm sleep disorder. For example, working nights can leave people in a constant readjustment cycle between their work hours and the hours they keep on non-work days for social activities, causing major sleep disruptions and potentially other health issues. Recent data has linked night shift work to increased risk of cardiovascular disease and even breast cancer in women.
Other circadian rhythm sleep disorders that affect the quality of sleep one gets are: delayed sleep phase syndrome (DSPS), which causes a much later than normal timing of sleep onset and offset and a period of peak alertness in the middle of the night; and advanced sleep phase syndrome (ASPS), which causes difficulty staying awake in the evening and staying asleep in the morning.
The key to getting a consistent good night’s rest is to keep a routine that keeps your circadian rhythm in harmony. If you feel you are keeping to routine, but still experience mid-day drowsiness or long periods of late-night alertness, talk to your health care provider and see if a sleep evaluation at our sleep center is appropriate for you.
Mark Reploeg, MD, is a board-certified neurologist, neurophysiologist, and sleep medicine specialist with The Corvallis Clinic. He is also the Medical Director of the Samaritan Sleep Disorders Center at Good Samaritan Regional Medical Center