Prevalence of and factors associated with vitamin D deficiency in 4,793 Japanese patients with rheumatoid arthritis

To determine the prevalence of vitamin D deficiency and associations with clinical characteristics in Japanese patients with rheumatoid arthritis (RA), serum 25(OH)D levels, laboratory data, and clinical data were obtained from 4,793 patients with RA (4,075 women, 718 men, mean age 59.7 years) who participated in the Institute of Rheumatology Rheumatoid Arthritis observational cohort study in April and May of 2011. Serum vitamin D levels were evaluated using a radioimmunoassay. We defined vitamin D deficiency as <20 ng/mL and severe deficiency as <10 ng/mL. Associations of vitamin D deficiency with patient characteristics were examined using multivariate logistic regression. Among all patients, the mean (SD) serum 25(OH)D level was 16.9 ng/mL (6.1), and the prevalence of vitamin D deficiency and severe deficiency were 71.8 and 11.5 %, respectively. In multivariate analysis, female gender, younger age, high Japanese version of health assessment questionnaire (HAQ) disability score, low serum total protein levels, low serum total cholesterol levels, high serum alkaline phosphate (ALP) levels, and non-steroidal anti-inflammatory drug (NSAID) use were significantly associated with vitamin D deficiency (P < 0.01). Vitamin D deficiency appears to be common in Japanese patients with RA, as previously reported for patients of other ethnicities. Female gender, younger age, high HAQ disability score, low serum levels of total protein and total cholesterol, high serum ALP levels, and NSAID use appear to be associated with vitamin D deficiency in Japanese patients with RA.