Dr. Chin Moi Chow
Sleep duration naturally waxes and wanes over a period of days.

This happens regardless of individual lifestyle, or timing of sleep or waking, says a new study from the University of Sydney in Australia.

"Sleep requirements vary in a cyclical fashion and between individuals. If you incur a sleep debt, your body will signal a need to catch up on extra sleep," notes Dr. Chin Moi Chow, principal investigator of the study.

Dr.Chow explains: "As you increase your sleep duration to recover from the debt, your ability to prolong wakefulness increases. Then, as prior wakefulness increases, sleepiness is inevitable, and a need for further sleep develops again."

Dr Chow and colleagues Shi Wong and Dr Mark Halaki, from the University's Faculty of Health Sciences, monitored a group of healthy young males.

To the researchers' fascination, the participants' sleep duration oscillated in a sine wave pattern - a phenomenon that had not previously been observed. Clear periodic patterns were found in the majority of the participants, varying from periods of between two and 18 days.

The sleep balance mechanism operates on an ongoing basis in daily life, with changes in sleep duration constantly accompanied by compensatory adjustments.

Variations in daily sleep duration may also arise from differences such as slight variations in the body clock or external factors like temperature, daylight, exercise, or eating and drinking patterns.

"Changing your sleep patterns on weekends, or resetting the pattern through shift work, could alter your sleep duration cycle and could put the body under significant strain," says Dr. Chow.

Source: Nature and Science of Sleep, January 2013 Volume 2013:5 Pages 1 - 6 "The periodicity of sleep duration - an infradian rhythm in spontaneous living" Wong SN, Halaki M, Chow CM,