Study Compares Ability Of Different Types Of Light To Shift Circadian Rhythms And Impact Sleep And Awake Schedules

Main Category: Sleep / Sleep Disorders / Insomnia
Article Date: 17 Apr 2009 - 1:00 PST

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The newer blue-enriched lights used in light boxes are no more effective at advancing circadian rhythms than the standard white lights that have been in use for decades according to a study by researchers in the Rush University Medical Center Biological Rhythms Research Lab. The study results will be published in the journal Sleep Medicine Vol. 10, issue 3 (April 2009).

These results are important for people who use therapeutic light boxes and scheduled exposure to light and darkness to rest their natural body clocks, such as shift workers and those who have certain sleep issues like delayed sleep phase disorder (DSPD), a condition in which an individual has a biological predisposition to go to bed and awaken on a much later schedule than most people.

Previous research has shown that the human circadian clock is most sensitive to short-wavelength (blue) light, but more research is needed regarding the dosage, timing and wavelength of light treatment.

Researchers at Rush were interested in finding out if bright blue lamps would provide a larger phase advance, or help patients awaken earlier, than the standard bright white lamps commonly used for phase shifting. The study found the blue lamps were no more effective than the standard bright therapy.

"This is good news for people using light treatment because it indicates that the standard white lights that are commercially available work as well as the newer blue-enriched lights. It means that patients are already likely getting a maximal therapeutic response, so there's no need to rush out and buy a new light box," said lead author Mark Smith, post-doctoral fellow in the Biological Rhythms Research Laboratory at Rush University Medical Center.

In the study, twenty-two healthy young adults received either a bright white or bright blue-enriched two-hour phase advancing light pulse upon awakening on each of four treatment days. On the first treatment day, the light pulse began eight hours after the dim light melatonin onset, on average about two hours before baseline wake time. On each subsequent day, light treatment began one hour earlier than the previous day, and the sleep schedule was also advanced.

Following the four treatment days, a final phase assessment was conducted. Phase advances of the blue-enriched and white groups were not significantly different.

The effectiveness of the blue-enriched lights at a different light level-less bright-for treatment of different clinical applications, was not tested in this study. According to study authors, blue-enriched lights may be useful for other clinical conditions.

The National Institutes of Health estimates that over 35 million Americans suffer from circadian rhythm disorders. Circadian rhythm disorders are the result of a mismatch between the body's internal clock and the external 24-hour schedule. The body clock needs to receive signals to tell it when to shut down and prepare for sleep and when to produce the active waking hormones. The most powerful signaler is bright light. Other signals include darkness, certain sounds, and mealtimes.

Rush University Medical Center is an academic medical center that encompasses the more than 600 staffed-bed hospital (including Rush Children's Hospital), the Johnston R. Bowman Health Center and Rush University. Rush University, with more than 1,270 students, is home to one of the first medical schools in the Midwest, and one of the nation's top-ranked nursing colleges. Rush University also offers graduate programs in allied health and the basic sciences. Rush is noted for bringing together clinical care and research to address major health problems, including arthritis and orthopedic disorders, cancer, heart disease, mental illness, neurological disorders and diseases associated with aging.

Source
Rush University Medical Center

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