Changes in iron metabolism during prolonged repeated walking exercise in middle-aged men and women

Abstract

PurposeThe aim of the present study was to assess the effect of prolonged and repeated exercise on iron metabolism in middle-aged adults and to compare differences between sexes.Methods50 male (58.9 ± 9.9 year) and 48 female (50.9 ± 11.2 year) individuals were monitored on 4 consecutive days at which they walked on average 8 h and 44 min per day at a self-determined pace. Blood samples were collected 1 or 2 days prior to the start of the exercise (baseline) and every day immediately post-exercise. Samples were analysed for iron, ferritin, haemoglobin, and haptoglobin concentrations.ResultsPlasma iron decreased across days, while ferritin increased across days (both p < 0.001). Haptoglobin showed a decrease (p < 0.001) after the first day and increased over subsequent days (p < 0.001). Haemoglobin did not change after the first day, but increased during subsequent days (p < 0.05). At baseline, 8% of the participants had iron concentrations below minimum reference value (10 µmol/L), this increased to 43% at day 4. There was an interaction between sex and exercise days on iron (p = 0.028), ferritin (p < 0.001) and haemoglobin levels (p = 0.004), but not on haptoglobin levels.ConclusionThis study showed decreases in iron, increases in ferritin, a decrease followed by increases in haptoglobin and no change followed by increases in haemoglobin. This is most likely explained by (foot strike) haemolysis, inflammation, and sweat and urine losses. These processes resulted in iron levels below minimum reference value in a large number of our participants.

Red Blood Cell Aging as a Homeostatic Response to Exercise-Induced Stress

“…It is possible that this increased susceptibility to oxidation is responsible for the small increase in hemolysis. This is in line with the decrease in haptoglobin and increase in ferritin after the first march day [13].…”

“…In conclusion, our data support the hypothesis that exercise causes various forms of physiological stress such as oxidation, increased shear stress, and inflammation [2,8,13,14] that induce an acceleration of the removal of the oldest, most susceptible RBCs. This occurs already during the first day of prolonged moderate-level exercise and may represent an early homeostatic adaptation leading to a functionally improved RBC population.…”

“…We postulate that this response results in a shift towards an overall younger RBC population, caused by accelerated aging and disappearance of the oldest cells from the circulation. These processes may be responsible for the changes in hemoglobin content starting on the first marching day [13]. The main findings that support this hypothesis are an increase in cell volume (Figure 1) with an accompanying shift in cell density (Supplementary Material Figure S1).…”

“…This provides an excellent opportunity to investigate the molecular mechanisms involved in the aging process of human RBCs in vivo. Our present data from a relatively small but representative number of subjects [1,13,14,18] indicate that participation in this event induces an early homeostatic response in the participants' RBCs. We postulate that this response results in a shift towards an overall younger RBC population, caused by accelerated aging and disappearance of the oldest cells from the circulation.…”

“…The Four Days Marches of Nijmegen in the Netherlands, the world's largest yearly voluntary walking event, presents the possibility to study the effect of prolonged, moderate-intensity exercise on the molecular mechanism of RBC aging in vivo. Recent observations in Four Days Marches participants on iron metabolism and cytokine responses have provided indirect indications that changes in the RBC population are involved in the physiological adaptation to prolonged exercise [11][12][13][14]. We postulate that these changes consist of an accelerated disappearance of the oldest RBCs, resulting in a functionally improved RBC population.…”