Influence Of Menstrual Cycle On Intestinal Injuries And Gastrointestinal Symptoms During Endurance Exercise

PURPOSE: Strenuous exercise induces intestinal injury and may be associated with gastrointestinal complaints reported during exercise. Several studies have found a greater incidence of gastrointestinal symptoms in women than in men who are engaged in endurance exercise, suggesting that sex hormones may contribute to this increase. However, in eumenorrheic women, the blood concentrations of female sex hormones change significantly during each monthly cycle. Therefore, this study aimed to investigate the influence of menstrual cycle on intestinal injuries and gastrointestinal symptoms during endurance exercise in eumenorrheic women. METHODS: The study participants were 11 eumenorrheic women (age, 20.4 ± 0.6 years; height, 157.9 ± 1.3 cm; weight, 52.8 ± 4.8 kg) who were engaged in habitual, recreational exercise. All the participants exercised by cycling at 70% Wmax for 60 minutes during the early follicular phase (E-FP), late follicular phase (L-FP), and luteal phase (LP). Serum estradiol, progesterone, and intestinal fatty acid binding protein (I-FABP) concentrations and gastrointestinal symptoms (13 items) were assessed before exercise (PRE), immediately after exercise (POST0), and 60 minutes after exercise (POST60). RESULTS: Serum estradiol concentrations were significantly higher in the L-FP and LP than in the E-FP at PRE (E-FP, 42.2 ± 14.1 pg/mL; L-FP, 155.6 ± 59.1 pg/mL; LP, 207.1 ± 88.6 pg/mL; p < 0.01). Serum progesterone concentrations were significantly higher in the LP than in the E-FP and L-FP at PRE (E-FP, 0.2 ± 0.1 ng/mL; L-FP, 0.6 ± 0.6 ng/mL; LP, 16.4 ± 6.6 ng/mL; p < 0.01). However, serum I-FABP concentrations and gastrointestinal symptoms did not significantly differ across menstrual cycle phases at PRE, POST0, or POST60 (I-FABP, menstrual cycle: p = 0.38, time: p < 0.01, menstrual cycle × time: p = 0.31; gastrointestinal symptoms, menstrual cycle: p > 0.05). Moreover, stomachache, stomach discomfort, and stomach burn (3 of the 13 items evaluated gastrointestinal symptoms) in the LP were significantly lower at POST0 and POST60 than at PRE (p < 0.05 for both). CONCLUSION: Our results suggest that the menstrual cycle does not influence intestinal injury markers and gastrointestinal symptoms during endurance exercise in eumenorrheic women.