Chronotype, social jetlag, sleep quality, and somatic symptoms in medical students: A serial mediation analysis

Chronotype and social jetlag are important correlates of sleep and health, yet their joint relationship with somatic symptom burden remains insufficiently studied in medical students. This cross-sectional study examined the associations among chronotype, social jetlag, sleep quality, and somatic symptoms in 500 undergraduate medical students aged 18-26 y. Chronotype was assessed with the Morningness-Eveningness Questionnaire (MEQ), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), social jetlag (SJL) from weekday-weekend mid-sleep differences, and somatic symptoms with the DSM-5 Level 2-Somatic Symptom-Adult scale. Higher morningness was associated with lower social jetlag, better sleep quality, and fewer somatic symptoms. Social jetlag was positively associated with poorer sleep quality and higher somatic symptom scores, whereas sleep quality showed the strongest association with somatic symptoms. In multivariable analyses, higher morningness predicted lower social jetlag and better sleep quality, and greater social jetlag independently predicted poorer sleep quality. However, after accounting for sleep quality, neither chronotype nor social jetlag remained independently associated with somatic symptoms. Serial mediation analysis showed that the chronotype-somatic symptom association was largely accounted for by indirect pathways, predominantly through sleep quality, with an additional smaller serial pathway through social jetlag and sleep quality.