ABSTRACT. Objectives: The aim of this study was to examine the association between dephospho-uncarboxylated matrix Gla protein (dp-ucMGP), an indicator of vitamin K status, and cognitive decline, and the modifying role of 25(OH)D. Design: Longitudinal study with six years follow-up. Setting: Community based. Participants: 599 participants of the Longitudinal Aging Study Amsterdam (aged 55-65 years). Measurements: Information processing speed and a composite Z-score by combining three domains of cognition reflecting general cognitive functioning. Results: Generalized estimating equations (GEE) showed no significant associations between dp-ucMGP and decline in general cognitive functioning. Vitamin D modified the association between dp-ucMGP and speed of information processing (p<0.05). In the group with a 25(OH)D concentration > 50 nmol/l, the highest tertile of dp-ucMGP (>406 pmol/l), which corresponds to lower vitamin K levels, was associated with 1.5 higher score on information processing speed (p=0.023) as compared to the lowest tertile of dp-ucMGP. Conclusion: In contrast to our hypothesis, a suboptimal vitamin K was not associated with cognitive decline in middle-aged adults.
