The association between vitamin D and C-reactive protein levels in patients with inflammatory and non-inflammatory diseases.

Objective: A direct, inverse correlation between 25-hydroxy vitamin D (25(OH) vitamin D) levels and C-reactive protein (CRP), a sensitive biomarker for inflammation, was found in some, but not all, studies. These effects were seen in healthy subjects as well as in some inflammatory diseases.

Design And Methods: CRP and 25(OH) vitamin D data (2011-2013) from 923 in- and outpatients (males/females 340/583; median age: 76years (95% confidence interval (CI): 75-77) were analyzed. A standardized diagnosis according to the Dutch diagnosis coding standard for each patient was obtained. Each diagnosis was categorized as either inflammatory or non-inflammatory disease. Analysis of variance was performed with age, gender, inflammatory status (inflammatory disease/non-inflammatory disease), and season as corrective factors.

Results: The correlation between (log) ln-25(OH) vitamin D and ln-CRP was highly significant (p<0.001) with a regression coefficient of -0.879. In the inflammatory disease group, the R(2) value was 0.726 and in the non-inflammatory disease group it was 0.502. It was shown that increasing 25(OH) vitamin D levels are associated with decreasing CRP levels, with a stronger effect in the inflammatory disease group compared to the non-inflammatory disease group.

Conclusions: Our study shows an inverse correlation between 25(OH) vitamin D and CRP in a large patient cohort but more importantly shows that this effect is more pronounced in patients with inflammatory diseases compared to patients with non-inflammatory diseases.