Insulin‐like growth factor‐binding protein 1 and blood rheology in athletes

The GH–IGF axis has been recently suggested to modulate blood rheology in trained athletes, via GH effects on body water status and a possible action of IGF‐I on erythrocyte deformability and aggregability. Another potential candidate for such a rheologic effect of the GH–IGF axis is insulin‐like growth factor binding protein‐1 (IGF‐BP1) which is increased in trained people and correlated to fitness: IGF‐BP1 is elevated in patients with polycythemia vera and stimulates erythroid burst formation in vitro. We investigated the statistical relationships between IGF‐BP1 and blood rheology in athletes. 21 soccer players, age 24.5±1.13 yr; body mass index 23.7±0.38 kg/m²; VO_2max 44.8±7 ml.min⁻¹.kg⁻¹). The major statistical determinant of IGFBP1 (measured at rest after overnight fast) was age (r=0.752, p=0.00013) which was not correlated with rheological parameters. IGF BP1 was negatively correlated with blood viscosity η (high shear rate r=−0.516, p=0.024) and positively correlated with the percentage of extracellular water in total body water (ECW/TBW) (r=0.488, p=0.039). The previously reported correlations between IGF‐I and both η (r=0.637, p=0.003) and red cell rigidity “Tk” (r=0.696, p=0.0137) were observed, but IGF‐I and IGF‐BP1 were not correlated to each other (r=−0.176 ns) and their correlations with η and Tk appeared to be independent when studied by multivariate analysis. Consistent with these correlations, subjects in the upper tertile of IGF‐BP1 (>23.4 ng/ml) compared to those in the lower (<7.5 ng/ml) had a higher percentage of ECW/TBW (40.8±0.4 vs 38±0.8%, p=0.033), a lower η (2.7±0.05 vs 2.97±0.06 mPa.s, p=0.016), and a lower Tk (0.54±0.05 vs 0.63±0.01, p=0.027). Thus, beside GH and IGF‐I, IGF‐BP1, which is reported to act on erythroid progenitors, exhibits statistical relationships with blood fluidity and erythrocyte flexibility that may suggest a physiological role in improving blood rheology.