Biological and social rhythm differences, daily melatonin secretion and psychiatric symptoms in healthy adults

Objective: To examine associations of chronotype and social jetlag (SJL) with psychiatric symptoms and melatonin secretion in healthy adults. Methods: In this cross-sectional study, 95 relatively young, university-affiliated students and staff completed the MEQ, SCL-90-R, MCTQ and a one-week sleep diary. SJL was defined as the workday–free-day difference in midsleep. Overnight workday urinary 6-sulfatoxymelatonin (6-SMT) was assayed by ELISA and indexed to creatinine. Results: Evening chronotypes had longer SJL than intermediate and morning chronotypes (F = 16.70, p < .001). Higher MEQ scores were associated with shorter SJL and earlier midsleep (r = −0.54 to −0.66, all p < .001). Total SCL-90-R scores did not differ across chronotypes (p = .367), whereas obsessive–compulsive symptoms were higher in the evening group (p = .027). Urinary 6-SMT/creatinine did not differ by chronotype (F = 0.823, p = .442) or relate to SJL; BMI correlated inversely with 6-SMT (r = −0.21, p = .043). Lower MEQ scores independently predicted longer SJL (B = −2.82, β = −0.54, p < .001). Conclusions: Eveningness was associated with greater SJL and obsessive–compulsive symptoms, whereas overnight 6-SMT was not linked to chronotype or SJL. The inverse BMI–6-SMT association may suggest metabolic relevance.