Effect of vitamin D on inflammatory and clinical outcomes in patients with rheumatoid arthritis: a systematic review and dose-response meta-analysis of randomized controlled trials.

There was no significant difference between the effect of 2 vitamin D doses on ESR and DAS28. To minimize the high heterogeneity among studies in this meta-analysis, other confounding factors such as baseline vitamin D, age, dietary vitamin D, time of year, sun exposure, drug interaction, effect dosage, and power of study should be examined.