Magazine article Nutrition Health Review

Resetting the Internal Clock When Seasons Change

Magazine article Nutrition Health Review

Resetting the Internal Clock When Seasons Change

Article excerpt

Resetting the Internal Clock When Seasons change

Scientists have found that carefully timed exposure to bright lights might prove a quick and effective treatment for certain sleep disorders.

Charles Czeisler, M.D., Ph.D., Richard Kronauer, Ph.D. and their colleagues at Brigham and Women's Hospital and Harvard University report that the body's internal clock is more sensitive to light than previously thought and can be "set" by scheduled exposure to light over a relatively short period of time.

Located in the brain's hypothalamus, this internal clock, or circadian pacemaker, controls when we sleep and when we wake, as well as a variety of other bodily activities which influence the way we think, feel and function. Each day, the pacemaker -- which runs on a cycle of about 25 hours -- is reset to fit the 24-hour cycle of the calendar day. Czeisler and his colleagues have found that light may be the single most important factor in resetting the clock and that the timing of light exposure determines the extent and direction of the change.

As part of their research, the investigators conducted a total of 45 trials in 14 healthy young men. For an average eight-day trial, each subject lived in a laboratory environment devoid of all external time cues. For the first two days of the trial, the subjects were kept awake while the investigators performed tests of body temperature, kidney function, alertness and performance to determine the normal setting of their pacemakers. They then experienced three days of alternating light (16 hours) and darkness (8 hours). For 5 hours during each light cycle the volunteers sat facing a bank of specially designed fluorescent lamps with an intensity comparable to sunlight just after dawn.

As a result, the investigators found that the human circadian pacemaker can be reset to any desired phase by scheduled exposure to light for 2 to 3 days. …

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