Vitamin D, a pro-hormone, is thought to play a potential immune-suppressive role, and to exert endocrine action on the immune system cells, generating anti-inflammatory and immunomodulatory effects. This study was designed to better understand the relationship between vitamin D and rheumatoid arthritis (RA).

The study was a post hoc analysis of data collected for the Comorbidities in Rheumatoid Arthritis (COMORA) study, an observational, cross-sectional, multicenter, international study of adults with RA. Data were collected for 1，413 patients from 15 countries. Demographic characteristics and disease specific variables were reported, including drug use and vitamin D supplementation. Disease activity was evaluated by DAS28 scores, characterized as high, moderate, low or in remission. In addition, functional impact of the disease was evaluated by the Health Assessment Questionnaire (HAQ). Current vitamin D levels were collected, and characterized as normal if Vitamin D levels were 30 ng/mL or more, insufficient if 10 to 30 ng/mL and deficient if <10 ng/mL.

The status of vitamin D levels was normal in 36.9%, insufficient in 54.6% and deficient in 8.5% of the subjects. Normal vitamin D status was found in over 50% of patients only in the United States and Italy, and in zero percent of those in Egypt, the Netherlands and the United Kingdom. Vitamin D levels were inversely correlated with DAS28 scores (<0.001).

This multi-national study of patients with rheumatoid arthritis found an inverse association between disease activity and vitamin D levels.