The vast majority of humans, as well as other animals, have a sleep-wake cycle that corresponds with the length of a day on Earth. We all sleep, awaken, and engage in our daily activities in accordance with our circadian rhythm, which is the daily cycle of biological activity based on a 24-hour period and influenced by regular variations in the environment, such as the alternation of night and day. Research has shown that the circadian rhythms of humans are actually slightly longer than 24 hours. It is difficult to pinpoint our circadian rhythms exactly, because to do so would require deprivation of sunlight, of our awareness of time, and of a number of other cues that help to regular the sleep-wake cycle. In everyday life, these cues are called zeitgebers, and daylight is the most influential.
Though I remember learning years ago in my introductory psychology class that the human circadian rhythm is approximately 25 hours, a study at Harvard University has shown that the normal human circadian rhythm may be much closer to 24 hours than scientists previously thought—approximately 24 hours and 11 minutes. Thus, the average person should have little trouble conforming to a 24-hour sleep-wake cycle. But what about the people who do not fall into the normal range?
Since I was a child, I have noticed that my pattern of sleeping and waking seems to constantly advance by an hour or two every night. This anomaly is very apparent during vacations from work and school. Without an alarm clock and daily obligations, I naturally fall asleep a little later each night, and get up a little later each morning. If my vacation is long enough, this continues until my sleep schedule is completely reversed, and I end up having to stay awake for 24 hours or so in order to reset my biological clock. I have often wondered if this problem of mine may be a real disorder with a biological basis. After doing some research, I have found that the answer is yes—I may suffer from non-24-hour sleep-wake syndrome.
Non-24-hour sleep-wake syndrome, also known as free running syndrome, is defined as a chronic steady pattern comprising of one- or two-hour delays in sleep onset and wake times in an individual living in society. In people with this disorder, the body basically insists that the day is longer than 24 hours and refuses to adjust to the external light/dark cycle. If left untreated, a person with non-24-hour sleep wake syndrome will have a sleep-wake cycle that changes every day. This is most commonly seen with blind individuals (nearly half of blind patients suffer from this condition), and it has also been observed in individuals who have sustained some sort of head injury. There have also been some studies of “normal” people who seem to have the syndrome. In one study, a subject with non-24-hour sleep-wake syndrome “appeared to be sub-sensitive to bright light,” which means that a possible cause for this disorder among sighted individuals could be that the body does not react to sunlight as it should.
The only way to know for sure if I have non-24-hour sleep-wake syndrome would be for me to be put away in a room for several days without sunlight, knowledge of time, or any other zeitgebers. Obviously, this would be impossible unless I am part of a clinical study, so I will have to assume that I may have this disorder. So, then what—what is the treatment? Experts say that the best a person with non-24-hour sleep-wake syndrome can do is to get plenty of sunlight in the morning and throughout the day, and take melatonin supplements or sleeping pills if needed at night, to allow one to conform to the 24-hour day.
Unfortunately for people like me, the Earth takes only 24 hours to spin once on its axis, and I have to somehow force my body to conform to that schedule. Perhaps if humans ever colonize Mars, I might be better off; a day on Mars lasts 24 hours and 40 minutes.
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Circadian rhythm sleep disorders. (2008). American Academy of Sleep Medicine. Retrieved November 22, 2010, from http://www.aasmnet.org/resources/factsheets/crsd.pdf
Cromie, W.J. (1999, July 15). Human biological clock set back an hour. Harvard Gazette. Retrieved November 22, 2010, from http://www.news.harvard.edu/gazette/1999/07.15/bioclock24.html.
McArthur, A. et. al. (1996). Non-24-hour sleep-wake syndrome in a sighted man: circadian rhythm studies and efficacy of melatonin treatment. Sleep. Volume 19, Number 7. Retrieved November 22, 2010, from PubMed Database.
The international classification of sleep disorders: diagnostic & coding manual. (2005). American Academy of Sleep Medicine. Retrieved November 22, 2010, from http://www.esst.org/adds/ICSD.pdf
Image retrieved November 22, 2005, from http://en.wikipedia.org/wiki/Mars.