Quantifying light-dependent circadian disruption in humans and animal models

Abstract

Although circadian disruption is an accepted term, little has been done to develop methods to quantify the degree of disruption or entrainment individual organisms actually exhibit in the field. A variety of behavioral, physiological and hormonal responses vary in amplitude over a 24-hour period and the degree to which these circadian rhythms are synchronized to the daily light-dark cycle can be quantified with a technique known as phasor analysis. Several studies have been carried out using phasor analysis in an attempt to measure circadian disruption exhibited by animals and by humans. To perform these studies, species-specific light measurement and light delivery technologies had to be developed based upon a fundamental understanding of circadian phototransduction mechanisms in the different species. When both nocturnal rodents and diurnal humans experienced different species-specific light-dark shift schedules, they showed, based upon phasor analysis of the light-dark and activity-rest patterns, similar levels of light-dependent circadian disruption. Indeed, both rodents and humans show monotonically increasing and quantitatively similar levels of light-dependent circadian disruption with increasing shift-nights per week. Thus, phasor analysis provides a method for quantifying circadian disruption in the field and in the laboratory as well as a bridge between ecological measurements of circadian entrainment in humans and parametric studies of circadian disruption in animal models, including nocturnal rodents.

Glucose tolerance in mice exposed to light–dark stimulus patterns mirroring dayshift and rotating shift schedules

“…Similarly, phasor magnitudes can be calculated for laboratory animals experiencing controlled cage-lighting patterns and wheel-running behavior patterns. As shown previously15, the same light–dark stimulus patterns actually experienced by people working dayshift and rotating shift schedules can be replicated with mouse-specific, calibrated light–dark stimulus patterns, yielding nearly identical phasor magnitudes27.…”

How to schedule night shift work in order to reduce health and safety risks

“…Night shift workers are exposed to light-at-night, which has earlier been proposed as one of the exposures linked with breast cancer through suppression of melatonin ( 10 ). Light-at-night is associated with lower levels of melatonin in both experimental ( 11 – 13 ) and observational studies of night shift workers compared with day workers ( 14 , 15 ). Animal studies show that alterations in the light–dark schedule suppress melatonin ( 3 ).…”

Non-visual effects of light: How to use light to promote circadian entrainment and elicit alertness

“…33 The authors’ quantitative comparison of these simplified functions, specifically concerning their ability to characterize the spectral sensitivity of nocturnal melatonin suppression using narrowband and polychromatic spectra, concludes that accuracy is lost when predicting light-induced nocturnal melatonin suppression by narrowband and broadband spectra. 34…”