Understanding how circadian biology varies across underrepresented populations matters more than it might appear. Most chronotype research has been conducted in Western Europe, North America, and East Asia — regions whose sleep-wake norms now shape global health guidelines, school start times, and workplace schedules. Data from Arab-majority and low-income countries remain scarce, creating blind spots in how circadian science is applied universally.
This study from Yemen, the first of its kind from that country, applied the validated Morning Evening Questionnaire (MEQ) to a cohort of young adults to characterize their circadian phenotypes. The dominant finding was that the majority of participants fell into the intermediate or "neither" chronotype category — neither strongly morning-oriented nor strongly evening-oriented. A modest but discernible trend toward morningness emerged with advancing age within the young adult range, while no statistically significant sex-based differences in chronotype were detected. These results were broadly consistent with chronotype surveys conducted across other Arabic-speaking countries, suggesting some regional coherence in circadian patterning.
The broader significance of this work lies in what it contributes to chronotype epidemiology rather than any single dramatic finding. Chronotype misalignment — when an individual's internal clock is forced out of sync with social or environmental schedules — has been associated with elevated risks for metabolic syndrome, cardiovascular disease, mood disorders, and certain cancers. Populations whose baseline chronotype distributions have never been characterized cannot be meaningfully included in these risk models. The absence of a significant sex effect in this Yemeni cohort is noteworthy, as many Western studies report women skewing slightly toward morningness post-adolescence, though sample composition and sociocultural factors may influence this. Key limitations include the study's restriction to young adults and reliance on self-report via questionnaire rather than actigraphy. This is an incremental but foundational contribution — filling a geographic gap in global chronobiology rather than rewriting existing theory.
