Relationships between blood viscosity and insulin‐like growth factor I status in athletes

Abstract

Exercise training is known (1) to enhance the function of the GH–IGF‐I system, which has profound effects on body fluid status; (2) to increase blood fluidity. Thus, we investigated during an exercise‐test in 39 male elite sportsmen (age 23.7±0.72 years; body mass index 23.7±0.28 kg/m²) the possible relationships between GH and IGF‐I status and the rheological properties of blood. Two correlations indicate a relationship between body hydration and fitness: isometric handgrip strength is correlated with the percentage of extracellular water in total body water (r=0.432, p=0.02) and the aerobic working capacity W₁₇₀ is negatively correlated with hematocrit (r=−0.341, p=0.039). Water loss during exercise appears to be inversely related to fitness as evaluated by W₁₇₀ (r=−0.529, p=0.05), and is positively correlated with the score of signs of overtraining (r=0.725, p=0.003) and with the red boood cell aggregation index (r=0.584, p=0.036). Finally, while the GH peak value is correlated with the extracellular water volume (r=0.393, p=0.02), IGF‐I is correlated with blood viscosity (r=0.546, p=0.0003), suggesting that when IGF‐I values are within the upper quintile (>340 ng/ml) IGF‐I may unfavourably affect blood rheology. Among factors of blood viscosity, IGF‐I exhibits a borderline correlation (p=0.05) with “Tk” and the ratio IGF1/IGFBP3 which reflects free circulating IGF‐I is correlated with red cell aggregability measured with the Myrenne “M” (r=0.485, p=0.014) and S₆₀ (r=0.396, p=0.494). These findings confirm the importance of hydration and dehydration as determinants of both blood rheology and exercise performance. Moreover, they suggest that values of IGF‐I within the upper quintile are associated with an impairment of blood fluidity, possibly due to a direct effect of IGF‐I on red cell deformability and aggregability.