Background: Large epidemiological studies confirm that brachial BP is positively related to red blood cell (RBC) count, hematocrit and hemoglobin. Despite several mechanisms being put forward, there are not yet a clear understanding on the interactions between erythrocytes and the arterial wall. Recent studies suggest BP lowering functions of RBCs by demonstrating that erythrocytes carry endothelial NO synthase, and that RBCs release ATP that triggers NO release. We assessed how central and brachial pressures, as well as arterial stiffness relate to RBC indices in healthy conditions within a young normotensive bi-ethnic population.

Methods: We included 328 black and white men and women aged 20–30 yrs. We performed full blood counts and assessed brachial (bSBP, DBP, Dinamap Procare 100) and central pressure (cSBP) and pulse wave velocity (PWV; Sphygmocor XCEL).

Results: Black participants (N=121) aged 25.2 yrs had higher bSBP (117/80 mmHg vs 113/77 mmHg) and cSBP (110 vs 105 mmHg) than white participants (N=207) aged 26.1 (all p≤0.001), with similar RBC counts (p=0.40). In multivariable-adjusted regression analyses cSBP related positively to RBC count in both groups (black: β=0.24; p=0.045; white: β=0.24; p=0.006) - not seen for bSBP (black: β=0.09; p=0.36; white: β=0.03; p=0.68). Only the black group showed independent associations of DBP with RBC count and hematocrit (p≤0.002), whereas PWV did not relate to RBC indices in any group.

Conclusions: We found that cSBP, but not bSBP, is positively associated with RBC count in a young normotensive bi-ethnic sample, suggesting that central haemodynamics may be more affected by increasing RBCs.