Crosstalk Between Environmental Light and Internal Time in Humans

Abstract

Daily exposure to environmental light is the most important zeitgeber in humans, and all studied characteristics of light pattern (timing, intensity, rate of change, duration, and spectrum) influence the circadian system. However, and due to lack of current studies on environmental light exposure and its influence on the circadian system, the aim of this work is to determine the characteristics of a naturalistic regimen of light exposure and its relationship with the functioning of the human circadian system. Eighty-eight undergraduate students (18-23 yrs) were recruited in Murcia, Spain (latitude 38°01'N) to record wrist temperature (WT), light exposure, and sleep for 1 wk under free-living conditions. Light-exposure timing, rate of change, regularity, intensity, and contrast were calculated, and their effects on the sleep pattern and WT rhythm were then analyzed. In general, higher values for interdaily stability, relative amplitude, mean morning light, and light quality index (LQI) correlated with higher interdaily stability and relative amplitude, and phase advance in sleep plus greater stability in WT and phase advance of the WT circadian rhythm. On the other hand, a higher fragmentation of the light-exposure rhythm was associated with more fragmented sleep. Naturalistic studies using 24-h ambulatory light monitoring provide essential information about the main circadian system input, necessary for maintaining healthy circadian tuning. Correcting light-exposure patterns accordingly may help prevent or even reverse health problems associated with circadian disruption.

Caffeinated Drinks Intake, Late Chronotype, and Increased Body Mass Index among Medical Students in Chongqing, China: A Multiple Mediation Model

“…Moreover, the effect of physical activity and inactivity time on the chronotype scores was notable. In previous studies, light exposure was considered an important zeitgeber in circadian systems [51], which can affect melatonin secretion and extend the entrainment phase, thereby developing late chronotypes [52,53]. In the university, students will spend more time staying indoors (such as classrooms, and dorms) than outdoors, and they generally experience a zeitgeber reduction because they are exposed to less light during the daytime, and the people with additional physical activities have a considerably higher possibility of light exposure.…”

The Characterization of Biological Rhythms in Mild Cognitive Impairment

“…Participants were instructed to wear the luxometer over their clothing and to leave it on the bedside table as they slept, according to previously described methodology [19]. …”

Clock Genes and Clock-Controlled Genes in the Regulation of Metabolic Rhythms

“…The daily entrainment to light is a critical mechanism to maintain bodily functions synchronized with the external environment Martinez-Nicolas et al, 2011). On the other hand, the liver plays a key role in the coordination of metabolic processes to daily feeding/fasting cycles, considering that intrinsic oscillation of clocks in liver cells can be entrained by food consumption (Vollmers et al, 2009), whereas oscillation of the brain clock is resilient and entrained primarily by light, which, in turn, acts through the brain clock to control feeding time (Koch et al, 2009).…”