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

• Vitamin D and CRP are inversely correlated in patients.
• Vitamin D is more strongly correlated with CRP in patients with inflammatory diseases.
• Vitamin D levels do not differ between inflammatory and non-inflammatory diseases.

ObjectiveA 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 methodsCRP and 25(OH) vitamin D data (2011–2013) from 923 in- and outpatients (males/females 340/583; median age: 76 years (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.ResultsThe 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 R2 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.ConclusionsOur 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.