Contemporaneous and temporal interrelationships between menstrual fluctuations in sex hormones and DXA estimates of body composition in a premenopausal female: a case study.

The reliability of dual energy X-ray absorptiometry (DXA) to assess body composition is influenced by factors like hydration status. Hence, any factor affecting total body water (TBW) content, such as menstrual shifts in sex hormones, might influence DXA estimates of lean soft tissue (LST) and fat mass (FM). To address this possibility, interrelationships between menstrual fluctuations in sex hormones, LST and FM were examined in a premenopausal female. The participant was monitored over 40 consecutive days for LST, FM and TBW by bioelectrical impedance. Daily capillary blood samples were taken to track 17β-estradiol, progesterone, and luteinizing hormone (LH). Using a graphical vector autoregression model, variable interrelationships were tested in a contemporaneous network (same measurement window) and temporal network (next measurement window). In the contemporaneous network, LST was related to TBW (r=0.42) and FM (r=-0.34). The temporal network uncovered directional effects of TBW (r=0.14), FM (r=-0.59) and LST (r=-0.50) on progesterone concentration. Hormonal interrelationships also emerged in the temporal network, whereby LH (r=0.24) and 17β-estradiol (r=0.13) were related to progesterone, and each hormone was related (r=0.50-0.69) to itself. The menstrual profiling of a premenopausal female revealed interrelationships between body composition and water content, but sex hormone fluctuations did not correlate with TBW, FM and LST on the same day or following day in the hypothesized direction. The temporal between- and within-hormone linkages reflect those natural feedback loops that control hormone secretion.