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Light & Health

New Approach Sheds Light on Ways Circadian Disruption Affects Human Health

A study by LRC researchers provides a new framework for studying the effects of circadian disruption on breast cancer, obesity, sleep disorders, and other health problems.

Experiment

LRC researchers have created a small, head-mounted device to measure an individual’s daily rest and activity patterns, as well as exposure to circadian light — short-wavelength light, particularly natural light from the blue sky, that stimulates the circadian system. The device, called the Daysimeter, was sent to 43 female nurses across the country to measure their daily exposure to circadian light.

The Daysimeter was worn for seven days by both day-shift and rotating shift nurses and then returned to the LRC for analysis. Researchers also studied the effect of irregular light exposure to the circadian system of 40 rats, in order to determine if the relationship between circadian disruption and health outcomes could be uncovered using rodent models.

Twenty rats were exposed to a consistently repeating pattern of 12 hours of light followed by 12 hours of dark, to mimic the light exposure experienced by day-shift workers. The remaining rodents were exposed to irregular 12-hour patterns of light and darkness. 

For the nurses, circadian entrainment and disruption was measured by comparing exposure light and darkness with each individual’s rest and activity patterns. Wheel running was used to measure rat rest and activity patterns. 

Results

Scientists quantified circadian behavioral entrainment or disruption using circular cross-correlations of activity and light exposure data. They found that the circadian entrainment and disruption patterns for day-shift and rotating shift nurses were remarkably different from each other, but remarkably similar to the patterns for the two parallel groups of nocturnal rodents. The marked differences within species suggest that health-related problems associated with humans can be studied using animal models.

Publications

Sponsors

Centers for Disease Control and Prevention

Trans-National Institutes of Health Genes, Environment and Health Initiatives

 


 

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