Menstrual phase and ambient temperature do not influence iron regulation in the acute exercise period

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 320; no. 6; pp. R780 - R790
• Main Authors: Zheng, Huixin, Badenhorst, Claire E, Lei, Tze-Huan, Liao, Yi-Hung, Che Muhamed, Ahmad Munir, Fujii, Naoto, Kondo, Narihiko, Mündel, Toby
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.06.2021
• Subjects: Ambient temperature; Body mass; Ferritin; Heat stress; Heat tolerance; Hepcidin; Humidity; Inflammation; Interleukin 6; Iron; Leukocytes; Menstrual cycle; Menstruation; Multiple regression analysis; Physiological effects; Physiology; Relative humidity; Water intake; Water intakes; heat stress; fluid balance; iron regulation; menstrual cycle
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00014.2021

The current study investigated whether ambient heat augments the inflammatory and postexercise hepcidin response in women and if menstrual phase and/or self-pacing modulate these physiological effects. Eight trained females (age: 37 ± 7 yr; V̇o : 46 ± 7 mL·kg ·min ; peak power output: 4.5 ± 0.8 W·kg ) underwent 20 min of fixed-intensity cycling (100 W and 125 W) followed by a 30-min work trial (∼75% V̇o ) in a moderate (MOD: 20 ± 1°C, 53 ± 8% relative humidity) and warm-humid (WARM: 32 ± 0°C, 75 ± 3% relative humidity) environment in both their early follicular (days 5 ± 2) and midluteal (days 21 ± 3) phases. Mean power output was 5 ± 4 W higher in MOD than in WARM ( = 0.02) such that the difference in core temperature rise was limited between environments (-0.29 ± 0.18°C in MOD, < 0.01). IL-6 and hepcidin both increased postexercise (198% and 38%, respectively); however, neither was affected by ambient temperature or menstrual phase (all > 0.15). Multiple regression analysis demonstrated that the IL-6 response to exercise was explained by leukocyte and platelet count ( = 0.72, < 0.01), and the hepcidin response to exercise was explained by serum iron and ferritin ( = 0.62, < 0.01). During exercise, participants almost matched their fluid loss (0.48 ± 0.18 kg·h ) with water intake (0.35 ± 0.15 L·h ) such that changes in body mass (-0.3 ± 0.3%) and serum osmolality (0.5 ± 2.0 osmol·kgH O ) were minimal or negligible, indicating a behavioral fluid-regulatory response. These results indicate that trained, iron-sufficient women suffer no detriment to their iron regulation in response to exercise with acute ambient heat stress or between menstrual phases on account of a performance-physiological trade-off.