News Release 

Sensitivity of human circadian system to evening light

Proceedings of the National Academy of Sciences

Humans are more sensitive to evening light than previously thought, with large differences in sensitivity across individuals, a study suggests. Exposure to light after dusk is pervasive in the modern world, representing a potential source of circadian rhythm disruption. Sean Cain and colleagues exposed 55 healthy people, aged 18-30 years, to evening light for 5 hours. All participants were exposed to a baseline dim light (<1 lux) and light levels ranging from 10 to 2,000 lux. On average, melatonin was 50% suppressed by exposure to 24.6 lux, which is comparable to or lower than typical indoor lighting used at night. At light levels as low as 6 lux in the most sensitive individual, 50% melatonin suppression occurred; however, 50% melatonin suppression occurred at 350 lux in the least sensitive individual. In addition, exposure to light intensities of 10 lux, 30 lux, and 50 lux delayed the rise in melatonin by 22 minutes, 77 minutes, and 109 minutes, respectively. According to the authors, individual differences in sensitivity to light may be an important and underappreciated determinant of the circadian clock's role in human health and disease.

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Article #19-01824: "High sensitivity and interindividual variability in the response of the human circadian system to evening light," by Andrew Phillips et al.

MEDIA CONTACTS: Sean Cain, Monash University, Clayton, AUSTRALIA; tel: +61 399051194, +61 467387031; e-mail: <sean.cain@monash.edu>

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