Physical Activity and Menstrual Health Symptoms and Characteristics: A Systematic Review and Meta-Analysis of Observational Studies.

Introduction: There is some evidence that structured exercise may improve menstrual health outcomes; however, it is unclear if habitual or lifestyle physical activity (PA) is also a protective factor. This systematic review synthesizes existing observational studies examining associations between PA and menstrual health outcomes. Methods: Medline, Embase, Web of Science, and SportDiscus were searched to identify peer-reviewed, English-language articles examining associations between PA and menstrual health in observational studies. Random-effects meta-analyses of differences in menstrual health outcomes between no-to-low PA and medium-high PA groups were conducted where possible, and narrative synthesis was used where heterogeneity was too high. Results: Of 3,620 studies screened, 82 (n = 101,413 women) were included. Outcomes explored included symptoms, such as pain (n = 32 studies) and premenstrual syndrome (PMS; n = 33), and cycle characteristics, such as regularity (n = 20), cycle length (n = 14), bleed length (12=), flow (n = 10), and other "menstrual problems" (n = 7). Meta-analyses suggested lower PA levels were associated with higher odds of menstrual pain (1.67 [95% CI: 1.31-2.11]; 21 studies), PMS (1.22 [1.03-1.45]; 18 studies), and cycle irregularity (1.73 [0.92-3.24]; 11 studies). Associations between PA and bleed length, cycle length, and flow were mixed. Study quality was low (mean 3.3/7; SD: 1.1), with most studies relying on cross-sectional designs, self-reported PA measures, and inconsistent definitions of menstrual health outcomes. Conclusions: This review found strong evidence suggesting high PA levels are associated with reduced menstrual symptoms but mixed evidence for menstrual characteristics. Despite methodological limitations, PA appears to be a promising, low-cost, and accessible intervention for menstrual health. Future research should standardize methodologies, exploring PA types and intensities to develop effective guidelines for managing menstrual health.