A Light Touch Changes the Biological Clock

Article excerpt

A light touch changes the biological clock

Airline passengers leaving San Francisco for London might one day use a precisely timed dose of light to reset their biological clocks to English time and avoid debilitating jet lag, if future research confirms a study reported this week.

Scientists have just begun unraveling the complicated circadian rhythm that governs sleepiness, hormone levels and other daily cycles of the body. Three years ago, researchers in Boston described a case study in which a 66-year-old woman with a fast-running biological clock sat in front of bright lights each night before going to bed (SN: 8/30/86, p. 136). Just one exposure to light shifted many aspects of her circadian cycle -- a finding that surprised scientists, who believed the human biological clock was not very sensitive to light but instead relied on social cues.

The same research team now has completed a larger study designed to find out how people with normal sleep patterns react to different light patterns given at varying stages in their circadian cycles. Charles A. Czeisler, director of the Center for Circadian and Sleep Disorders Medicine at Brigham and Women's Hospital in Boston, and his colleagues studied 14 men aged 18 to 24. The subjects checked into the Boston sleep laboratory, where scientists charted their normal biological cycles using hormone levels and endogenous body temperature, a measure that corrects for subtle temperature fluctuations caused by activity. Subjects then went through three 24-hour cycles that included eight hours of darkness, 11 hours of indoor room light and five hours of bright light equivalent to sunlight. …