The effective oxygen diffusivity (EOD) of the capillary bed has gained increasing interest as a promising biomarker providing additional information on microvascular integrity. To overcome limitations in the applicability of existing and relatively complex EOD mapping techniques, we proposed a novel more easily applicable MR-based approach. We measured EOD in 16 young and 30 elderly healthy subjects. Our measurements of EOD by MRI in young subjects yielded comparably good results in comparison with PET-data as a reference. Furthermore, we found EOD reductions in elderly healthy subjects with concomitant capillary transit-time heterogeneity (CTH) increases, indicating disturbed capillary oxygen extraction ability.