Background Haemoglobin scavenges nitric oxide, and a previous study has shown a negative association between flow-mediated vasodilation (FMD), a measure of nitric oxide (NO)-dependent vasomotor function and haemoglobin concentrations [Hb]. Circulating erythropoietin (EPO) is also negatively associated with [Hb] and could influence availability of NO. The purpose of this study was to examine the association of FMD with [Hb] and EPO concentrations and to determine whether these contribute to the sex difference in FMD. FMD (by high-resolution ultrasound), [Hb], circulating immunoreactive EPO and cardiovascular risk factors were measured in 317 healthy middle-aged men and women (183 women, 33 premenopausal, mean age +/- SD, 55 +/- 6 center dot 8years) participating in a dietary study. Results In the whole mixed-sex group, FMD was negatively correlated with [Hb] (R=0 center dot 23, P<0 center dot 001). However, in a multivariable model, incorporating sex and other confounding factors, FMD was independently negatively correlated only with age, male sex and systolic blood pressure: standardized regression coefficients 0 center dot 21 (P<0 center dot 01), 0 center dot 17 (P<0 center dot 05) and 0 center dot 20 (P<0 center dot 05) respectively and not with [Hb]. Similarly, when the analysis was restricted to men or to postmenopausal women, there was no significant relationship between FMD and Hb. There was no significant correlation between FMD and EPO on either univariate analysis in the whole group, in each sex, or in multivariate analysis. Conclusion These results suggest that in healthy middle-aged subjects, FMD is not influenced by [Hb] or EPO and these do not contribute to the gender difference in FMD.
