Abstract

Vartanian, D. (2025). Is latitude associated with chronotype? [Master’s Thesis, University of São Paulo]. https://doi.org/10.17605/OSF.IO/YGKTS

Although much is known about circadian rhythms, further research with larger samples is needed to gain a better understanding of the expression of temporal phenotypes. This thesis investigates the hypothesis that latitude influences chronotype expression, based on the premise that polar regions receive less sunlight annually than equatorial regions. This difference in photoperiod suggests a stronger solar zeitgeber in equatorial areas, potentially leading to greater entrainment of circadian rhythms with the light/dark cycle. This, in turn, could reduce the amplitude and diversity of circadian phenotypes, resulting in a higher prevalence of morningness in equatorial populations. To test this hypothesis, data from \(65.824\) individuals across Brazil, collected in 2017 based on the Munich ChronoType Questionnaire (MCTQ), were analyzed using nested linear regression models. The analysis revealed a negligible effect of latitude on chronotype (Cohen’s \(f^2 = 0.0030818242\), \(95\% \ \text{IC}[0, 0.0121371208]\)), a finding that contrasts with recent studies. Although the hypothesis is plausible and consistent with evolutionary theories of temporal biological systems, these results suggest that the phenomenon of entrainment is more complex than previously assumed.

Keywords: Complexity science. Complex systems. Chronobiology. Biological rhythms. Chronotypes. Circadian phenotypes. Sleep. Entrainment. Latitude. MCTQ.