***Physical activity and BMI as modifiable factors influencing premenstrual symptoms: findings from 21 years of longitudinal data

Introduction:
Pre-menstrual symptoms (PMS) affect many women of reproductive age, negatively impacting quality of life, mood, and daily functioning. Both physical activity (PA) and body mass index (BMI) have been proposed as modifiable factors influencing PMS, but most research is cross-sectional or short-term. This study aimed to investigate the individual and combined associations of PA and BMI with PMS over 21 years in a large cohort of women, providing insights into long-term patterns and potential interactions. Methods: Participants (18-23 years in 1996; N=14,247) from The Australian Longitudinal Study of Women’s Health completed eight surveys from 1996 to 2018. They reported PA, weight and height and the frequency of PMS (never; rarely; sometimes; or often) in every survey from 2000 to 2018. BMI was calculated from self-reported weight and height. The individual and combined associations between PA and BMI with PMS from 2000 to 2018 were examined in a sample of 12,007 women using generalised estimating equations. Results: At baseline (2000), the prevalence of PMS
was 27%, highest in women who were nulliparous (87.2%), living in major cities (56.2%) and underweight/normal weight (67%). Meeting PA guidelines (≥500MET-min/week) was associated with lower odds of PMS (OR=0.92, 95% CI:0.86–0.98). Combined associations between PA and BMI showed active obese women had the lowest odds of PMS (OR=0.91, 95% CI:0.82–1.00). When explored
further, obese women who reported high PA had a 19% reduction in the likelihood of PMS (OR=0.81, 95% CI:0.67–0.97). Conclusions: Drawing on 21 years of longitudinal data, this study shows that PA lowers the odds of PMS, especially in women with obesity. These findings advance PA research by confirming its long-term benefit for women’s reproductive health and support targeted PA promotion to improve menstrual health and wellbeing.