Seasonal changes in haematology, lymphocyte transferrin receptors and intracellular iron in Ironman triathletes and untrained men

We investigated whether 12 months of chronic endurance training would affect haematology, CD4⁺ lymphocyte transferrin receptor (CD71) expression, CD4⁺ intracellular iron and the incidence of upper respiratory tract illnesses (URTI) in Ironman triathletes compared with untrained men. Resting venous blood samples were taken from 15 Ironman triathletes (TR 30 ± 5 year) and 12 untrained men (UT 30 ± 6 year) every 4 weeks for 12 months. Erythrocyte, leukocyte and platelet concentration, haematocrit, haemoglobin (Hb) and mean corpuscular haemoglobin (MCHC) were measured with a full blood count. CD4⁺ lymphocytes were analysed for changes in transferrin receptor (CD71) expression (CD4⁺CD71⁺), and intracellular iron (Fe³⁺), by flow cytometry. The TR group had significantly lower Hb, MCHC, and platelets for 10, 9 and 11 months, respectively; lower CD4⁺CD71⁺ (3 months) and Fe³⁺ (1 month), respectively; higher CD4⁺CD71⁺ (1 month); a higher lymphocyte count for 4 months. There were no between-group differences in other variables. In both groups haematology and lymphocytes increased during spring, early summer and winter and decreased during late summer/late winter, with an inverse relationship between CD4⁺CD71⁺ and Fe³⁺. The TR group reported significantly fewer URTI than the UT. Low Hb and MCHC suggest an iron deficiency which may affect triathlete performance. Monthly changes in lymphocytes, CD4⁺CD71⁺ and Fe³⁺ suggested that spring, summer and late autumn are associated with CD4⁺ proliferation. There may be seasonal relationships between haematology and lymphocyte function, independent of endurance training, possibly affecting performance but not the incidence of URTI.