Postprandial inflammation is considered to be pro-atherogenic. Vitamin D can reduce inflammation and arterial stiffness. We hypothesized that vitamin D3 improves postprandial arterial elasticity by the modulation of leukocyte activation. Healthy volunteers underwent two oral fat-loading tests (OFLTs). The augmentation index (AIx) and flow cytometric quantification of leukocyte activation markers were measured. After the first OFLT, 100 000 IU of vitamin D3 was administered and a second OFLT was carried out 7 days later. Six men and six women were included. A favorable reduction in AIx was found after vitamin D3 supplementation (P=0.042) in both genders. After vitamin D3, exclusively in women a reduction in the area under the postprandial curve for monocytes CD11b and CD35 by 10.5% (P=0.016) and 12.5% (P=0.04) and neutrophil CD11b by 17.0% (P=0.014) was observed. In conclusion, vitamin D3 probably increased postprandial arterial elasticity in men and women, but reduced postprandial leukocyte activation exclusively in women.