Chronotype score is associated with testosterone levels and estradiol-to-testosterone ratio in young adult Saudi women: a cross-sectional study

BACKGROUND: Chronotype reflects individual preference for sleep-wake timing and is closely linked to circadian rhythm regulation. Greater eveningness tendency has been associated with adverse metabolic and endocrine outcomes; however, evidence regarding its relationship with reproductive hormones in women remains limited, particularly in Saudi Arabia. This study aimed to investigate the association between chronotype score and gonadal hormone profiles in young adult Saudi women. METHODS: In this cross-sectional study, 58 healthy Saudi female university students aged 18-23 years were recruited at Jazan University between September and October 2025. Blood samples were collected during the early follicular phase of the menstrual cycle (days 2-5). Chronotype was assessed using the Reduced Morningness-Eveningness Questionnaire (rMEQ). Serum estradiol and testosterone concentrations were measured using chemiluminescent immunoassays. Associations between rMEQ score and hormonal parameters were evaluated using Spearman's rank correlation and partial Spearman correlation analyses. RESULTS: rMEQ score was negatively correlated with testosterone concentrations (ρ = -0.344, P = 0.008) and positively correlated with the estradiol-to-testosterone (E2/T) ratio (ρ = 0.338, P = 0.009), indicating that greater eveningness tendency was associated with a relatively more androgenic hormonal profile. These associations remained significant after adjustment for age, body mass index, and menstrual cycle day. No significant association was observed between rMEQ score and estradiol concentrations (ρ = 0.017, P = 0.897). CONCLUSIONS: Lower rMEQ scores, indicating greater eveningness tendency, were associated with higher testosterone concentrations and a reduced E2/T ratio in healthy young Saudi women, suggesting a relatively more androgenic hormonal profile. These findings indicate that variation in chronotype may be linked to differences in reproductive hormone balance and may have implications for women's reproductive and metabolic health.