Menstrual cycle irregularity is a biological determinant of mental health independent of sleep in adolescents

INTRODUCTION: Sex differences in mental health emerge during adolescence, a period marked by the onset and the establishment of menstrual cycle. However, is rarely examined how menstrual cycle regularity, a marker of hormonal function, modulates mental health. OBJECTIVE: to analyse sex differences in mental health symptoms among adolescents considering the menstrual cycle regularity and sleep. METHODS: A three-group design (female students with regular cycles/FR, n=77; with irregular cycles/FI, n=59; and male students/M, n=76) in a sample of Brazilian high-school adolescents (n=212; 14-18 years) enrolled in morning and full-time classes was used to test the hypothesis that mental health symptoms follow a graded pattern across these groups. RESULTS: Mean DASS-21 scores across all groups fell at or above the Mild severity threshold for mental health subscales. GLMs confirmed a monotonic gradient increase in group order (M[->]FR[->]FI) which was associated with higher scores on all outcomes (stress {beta}/step=4.33, p<.001; anxiety {beta}/step=4.08, p<.001; and depression {beta}/step=2.34, p=.010; model R{superscript 2}=.16, .13, .08 respectively). However, no differences were observed in sleep duration, social jetlag, chronotype, sleep quality, or sleep-debt. Then, a secondary analysis assessed sex-specific associations between socioeconomic status (SES) and mental health; higher SES was inversely related to stress, anxiety, and depression, being protective only in males (stress Males {beta}=-2.68, p=.011/Females {beta}=0.46, p=.614). CONCLUSION: These findings support the reframing of menstrual irregularity not only as a reproductive health concern but also as a biological determinant of mental health risk in female adolescents, a vulnerability that sleep disruption and socioeconomic resources do not adequately explain.