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 (Fe(3+)), 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 Fe(3+) (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 Fe(3+). 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 Fe(3+) 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.