Latitudinal cline of chronotype

Abstract

The rotation of the Earth around its own axis and around the sun determines the characteristics of the light/dark cycle, the most stable and ancient 24 h temporal cue for all organisms. Due to the tilt in the earth’s axis in relation to the plane of the earth’s orbit around the sun, sunlight reaches the Earth differentially depending on the latitude. The timing of circadian rhythms varies among individuals of a given population and biological and environmental factors underlie this variability. In the present study, we tested the hypothesis that latitude is associated to the regulation of circadian rhythm in humans. We have studied chronotype profiles across latitudinal cline from around 0° to 32° South in Brazil in a sample of 12,884 volunteers living in the same time zone. The analysis of the results revealed that humans are sensitive to the different sunlight signals tied to differences in latitude, resulting in a morning to evening latitudinal cline of chronotypes towards higher latitudes.

Delayed Sleep in Winter Related to Natural Daylight Exposure among Arctic Day Workers

“…From a chronobiological and light perspective, other scenarios have been discussed to explain seasonal differences. The sleep/wake cycle may be more delayed at high latitudes during summer than winter due to strong natural light exposure during the phase-delaying part of the Phase Response Curve [29,30]. In theory this would be the time of day when the core body temperature shows a decline.…”

Genome-wide association analyses of chronotype in 697,828 individuals provides new insights into circadian rhythms in humans and links to disease

“…Significant natural variation exists amongst the human population with chronotype often measured on a continuous scale 2 , though individuals are traditionally separated into "morning people" (or "larks") who prefer going to bed and waking earlier, "evening people" (or "owls") who perform best with a later bedtime and later rising time, and "intermediates" who lie between the two extremes 3,4 . Age and gender, as well as environmental light levels explain a substantial proportion of variation in chronotype, but genetic variation is also an important contributor 5,6,7,8 .…”

Duración subóptima del sueño y fenotipo circadiano en mujeres adultas residentes de Valencia, Venezuela atendidas en jornadas de salud. Perfil cardiometabólico asociado

“…La luz solar alcanza diferencialmente al planeta de acuerdo a la latitud. Un estudio realizado en el sur de Brasil reveló un gradiente latitudinal en los cronotipos según el cual se eleva la vespertinidad a medida que se incrementa la latitud o distancia angular entre la línea ecuatorial y un punto determinado de la Tierra (32) .…”