Menstrual Cycle Related Fluctuations in Circulating Markers of Bone Metabolism at Rest and in Response to Running in Eumenorrheic Females

Abstract

The aim of this study was to investigate potential fluctuations in bone metabolic markers across the menstrual cycle both at rest and after a 30-minute bout of vigorous-intensity running at 80% of �̇ O₂max. Resting and post-exercise (0, 30, 90 min) sclerostin (inhibitor of bone formation), parathyroid hormone (PTH, regulator of calcium homeostasis), carboxy-terminal cross-linking telopeptide of type I collagen (β-CTX, marker of bone resorption), and procollagen type 1 N propeptide (P1NP, marker of bone formation) were assessed in 10 young, eumenorrheic women (21.7 ± 3.2 years, 23.2 ± 3 kg. m2 ) during the mid- to late-follicular (FP: day 8.0 ± 1.4) and midluteal (LP: day 22.0 ± 2.5) phases of the menstrual cycle. Ovulation was determined using ovulation kits and daily measurement of oral body temperature upon awakening. Menstrual phase was subsequently confirmed by measurement of plasma estradiol and progesterone taken on study days, confirming an increase in both hormones during the mid-luteal phase. At rest, there were no significant differences in sclerostin (FP: 266.5 ± 48.6 pg·mL-1 ; LP: 296.0 ± 37.5 pg·mL-1 ; p=0.507), PTH (FP: 1.00 ± 0.22 pmol·L-1 ; LP: 0.71 ± 0.16 pmol·L-1 ; p=0.485), β-CTX (FP: 243.1± 52.7 ng·mL-1 ; LP: 202.4 ± 30.8 ng·mL-1 ; p=0.691), or P1NP (FP: 56.9 ± 11.30 ng·mL-1 ; LP: 64.30 ± 18.32 ng·mL-1 ; p=0.133) between menstrual cycle phases. As there were no main effects for menstrual phase and no significant interaction, post-exercise responses did not differ between menstrual phases for any of the markers. Significant main effects for time were found in sclerostin, PTH, β-CTX and P1NP. Specifically, sclerostin and PTH increased from pre- to immediately postexercise (+46% and +43%, respectively; p<0.0001), then returned to resting concentrations at 30 min post-exercise. P1NP also increased immediately post-exercise (+29%; p<0.0001), returning to resting concentrations at 30 min post-exercise. β-CTX decreased from pre- to immediately postexercise (-20%; p=0.004) and remained below its pre-exercise concentrations at 30 min postexercise (-12%; p=0.039) and 90 min post-exercise (-17%; p=0.002). These results demonstrate that sclerostin, PTH, β-CTX and P1NP do not differ at rest or in response to exercise across the menstrual cycle.