Magazine article Nutrition Health Review

Sleep Needs May Be Controlled Biologically

Magazine article Nutrition Health Review

Sleep Needs May Be Controlled Biologically

Article excerpt

You cannot fool "Mother Nature" when it comes to how much sleep a person requires, according to a recent study (Journal of Clinical Endocrinology and Metabolism, January 2003). Researchers at the National Institute of Mental Health in Bethesda, Maryland, found that sleep needs vary according to individual factors programmed by the body's internal clock.

"Our study shows that the body's internal clock programs a longer biological night in long sleepers than in short sleepers," said Dr. Daniel Aeschbach, lead author of the study at Brigham and Women's Hospital and Harvard Medical School in Boston. "Thus, individual differences in the clock's program may contribute to the variability in sleep duration in the general population. Although we do not know the origin of these differences, the present results provide a physiological basis for why it is difficult to change sleep habits willfully."

Researchers have long hypothesized that sleep duration (how long we sleep) has a physiological basis, driven by an internal signal. However, meaningful differences between long and short sleepers have never been identified. Recent analyses using an electroencephalogram, which provides a record of the electric potentials of the brain derived from electrodes attached to the scalp, during sleep and wakefulness have shown that short sleepers can live under higher "sleep pressure," or "sleep debt." This pressure increases during waking hours and decreases during sleep. Even so, the kinetics, or measure of change, of sleep pressure during sleep and wakefulness were similar in both short and long sleepers.

For this reason, the researchers decided to examine the output of the body's internal clock, called the circadian pacemaker. They hypothesized that the programming of this clock might be different in the two types of sleepers. The clock, which is located in the brain in the suprachiasmatic nucleus of the hypothalamus, programs daily cyclic changes in the body, thereby creating two distinct periods, a biological day and a biological night.

"During the biological night, the hormone melatonin is secreted, blood concentrations of the hormone cortisol increase, body temperature is lowered, and sleepiness and sleep propensity increase," explains Dr. Aeschbach.

To monitor these biological changes, the researchers studied 10 long sleepers and 14 short sleepers in constant environmental conditions while they stayed awake for 40 hours. …

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