Additionally, a significant inverse correlation was found between 25OHD and disease activity levels measured by DAS 28 (correlation coefficient: −0.084) as well as with C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) values (coefficient being –0.115 and −0.18, respectively), showing that lower 25OHD levels are associated with a higher prevalence and severity of RA [55]. Here, CRP is linked to rheumatoid arthritis.