This study examined postexercise inflammatory, hepcidin, and iron absorption responses to endurance exercise performed in the morning versus the afternoon.
Sixteen endurance-trained runners (10 male, 6 female) with serum ferritin (sFer) < 50 μg·L−1 completed a 90-min running protocol (65% vV˙O2max) in the morning (AM), or the afternoon (PM), in a crossover design. An iron-fortified fluid labeled with stable iron isotopes (57Fe or 58Fe) was administered with a standardized meal 30 min following the exercise and control conditions during each trial, serving as a breakfast and dinner meal. Venous blood samples were collected before, immediately after, and 3 h after the exercise and control conditions to measure sFer, serum interleukin-6 (IL-6), and serum hepcidin-25. A final venous blood sample was collected 14 d after each trial to determine the erythrocyte iron incorporation, which was used to calculate iron absorption. Linear mixed-modeling was used to analyze the data.
Overall, exercise significantly increased the concentrations of IL-6 (4.938 pg·mL−1; P = 0.006), and hepcidin-25 concentrations significantly increased 3 h after exercise by 0.380 nM (P < 0.001). During the PM trial, hepcidin concentrations exhibited diurnal tendency, increasing 0.55 nM at rest (P = 0.007), before further increasing 0.68 nM (P < 0.001) from prerun to 3 h postrun. Fractional iron absorption was significantly greater at breakfast after the AM run, compared with both the rested condition (0.778%; P = 0.020) and dinner in the AM run trial (0.672%; P = 0.011).
Although exercise resulted in increased concentrations of IL-6 and hepcidin, iron was best absorbed in the morning after exercise, indicating there may be a transient mechanism during the acute postexercise window to promote iron absorption opposing the homeostatic regulation by serum hepcidin elevations.
1School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Crawley, Western Australia, AUSTRALIA
2The Western Australian Institute of Sport, Mt Claremont, Western Australia, AUSTRALIA
3Laboratory of Human Nutrition, Department of Health Sciences and Technology, ETH Zürich, SWITZERLAND
4Australian Institute of Sport, Bruce, Australian Capital Territory, AUSTRALIA
5Translational Metabolic Laboratory, Radboud University Medical Centre, Nijmegen, THE NETHERLANDS
6Hepcidinanalysis.com, Nijmegen, THE NETHERLANDS
7Medical School, Fiona Stanley Hospital, University of Western Australia, Murdoch, Western Australia, AUSTRALIA
8Harry Perkins Institute of Medical Research, Murdoch, Western Australia, AUSTRALIA
9Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Queensland, AUSTRALIA
10Triathlon Australia, Gold Coast, Queensland, AUSTRALIA
11School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, AUSTRALIA
12Medical School, Royal Perth Hospital, The University of Western Australia, Perth, Western Australia, AUSTRALIA
13School of Health and Life Sciences, Federation University Australia, Ballarat, Victoria, AUSTRALIA
Address for correspondence: Rachel McCormick, McGillivray Rd, Mt. Claremont, Western Australia, 6010; E-mail: firstname.lastname@example.org.
Submitted for publication December 2018.
Accepted for publication April 2019.
Online date: May 2, 2019