EMBARGOED FOR RELEASE UNTIL 4 PM ET, April 18, 2002
Exposure to Light and Sleep Pattern Alteration Can Affect the Biological Clock
Denver, Colo. -
Each person''s circadian rhythm, or biological clock, influences when we are tired, hungry, more or less sensitive to drugs and other stimuli, and even cues the secretion of hormones throughout each 24-hour period. In a study presented at the 54th Annual Meeting of the American Academy of Neurology, researchers demonstrate the degree to which light exposure, as well as alterations in sleep patterns, can affect the timing of the circadian clock. Recent studies have shown that both the intensity and the timing of light are important to determining the magnitude of shifts in the circadian clock. "We were interested to know more about the response of the human biological clock to varying durations of light pulses," says study author Samir Bangalore, of Northwestern University Medical School in Chicago, Ill. For the study, 10 men and 22 women, average age 29, were admitted for two stays at a clinical research center, each lasting four nights and three days. On the first night, subjects maintained a constant daytime routine and slept for eight hours in the dark at their usual bedtime. Each of the following nights, subjects were awoken and exposed to varying intensities and durations (one, two, or three hours) of light, with a control group simply awakened for four hours each night. Circadian rhythms were measured by fluctuations in core body temperature and in levels of serum melatonin, a hormone believed to play a role in the circadian rhythm. According to Balgalore, "Our results indicate that a single pulse of bright light lasting just two to three hours is sufficient to delay human circadian rhythms." Furthermore, disruptions in sleep timing can also produce small rhythm delays. Together, these results show that duration of light exposure, in addition to light intensity and alterations in sleep patterns, can affect the timing of the circadian clock.