ORIGINAL ARTICLE The predictive factors of low serum 25-hydroxyvitamin D and vitamin D deficiency in patients with systemic lupus erythematosus Kittiwan Sumethkul • Smonporn Boonyaratavej • Tasanee Kitumnuaypong • Sungchai Angthararuk • Patcharin Cheewasat • Naruimon Manadee • Vasant Sumethkul Received: 21 February 2012 / Accepted: 21 October 2012 / Published online: 22 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012 Abstract Vitamin D is a steroid hormone with pleiotropic effects. The association between serum 25-hydroxyvitamin D level [25(OH) D] and lupus nephritis are not clearly known. We aim to determine serum 25(OH) D levels in patients with inactive SLE, active SLE without lupus nephritis (LN) and active SLE with LN and to identify clinical predictor of vitamin D deficiency. One hundred and eight SLE patients were included. Patients were classified as Group (Gr) 1, 2 and 3 if they had SLE disease activity index (SLEDAI) \ 3, C3 but no LN and C3 with LN. Important baseline characteristics were collected. 25(OH) D was measured by high performance liquid chromatog- raphy (HPLC). SLEDAI in Gr1, Gr2 and Gr3 was 0.7 (0.9), 5.6 (2.3) and 9.2 (5.2), respectively. 43.5 % had vitamin D insufficiency and 29.6 % had vitamin D deficiency. Mean 25(OH) D in each groups was 28.3 (8.0), 26.7 (9.5) and 19.9 (7.6) ng/ml (p \ 0.001 comparing Gr1 and 3) (p = 0.003 comparing Gr2 and 3). Vitamin D deficiency was found in 11.1, 22.2 and 55.6 % of Gr1, 2 and 3. Linear regression analysis found that 25(OH) D was significantly correlated with serum albumin (r = 0.28, p = 0.004), inversely correlated with SLEDAI (r =-0.22, p = 0.03) and urinary protein creatinine index (UPCI) (r =-0.28, p = 0.005), but not with sun exposure score, body mass index and estimated GFR. Only UPCI was significantly inversely correlated with 25(OH) D (p = 0.02) from mul- tiple linear regression. LN was a significant predictor of vitamin D deficiency from multivariate logistic regression (OR 5.97; p = 0.006). Vitamin D deficiency and insuffi- ciency was found in 93 and 86 % of LN with proteinuria C and \ 500 mg/day. We conclude that SLE patients with LN have significantly lower vitamin D level than inactive SLE and active SLE without LN. Hence, nephritis is a signifi- cant predictor of vitamin D deficiency in SLE patients. Keywords 25-Hydroxyvitamin D Á Vitamin D deficiency Á Serum 25(OH) D Á Systemic lupus erythematosus Á Lupus nephritis Á Proteinuria Investigations about the effect of vitamin D beyond bone health are increasing. These include the immunological effect of vitamin D on B lymphocyte, antigen presenting cell [1, 2] and cardiovascular effects [3]. The association between chronic kidney disease and vitamin D deficiency was demonstrated by the previous studies [4, 5]. Two recent randomized, controlled studies had demonstrated the benefit of vitamin D for reduction in proteinuria in diabetic nephropathy [6] and IgA nephropathy [7]. Previous studies had demonstrated lower vitamin D level in patients with SLE than age-match control [8]. Vitamin D deficiency is defined as serum 25(OH) D level less than 20 ng/ml [9]. The factors that may be associated with low vitamin D level in SLE patients are not clearly known. Previous studies showed that low vitamin D level in SLE patients was associated with high body mass index [10] and ethnic with dark skin color [11]. The association between SLE disease K. Sumethkul (&) Á T. Kitumnuaypong Á S. Angthararuk Á P. Cheewasat Á N. Manadee Rheumatology Unit, Department of Medicine, Rajavithi Hospital, 2 Rajavithi Road, Bangkok 10400, Thailand e-mail: ckittiwan@hotmail.com S. Boonyaratavej Division of Cardiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand V. Sumethkul Division of Nephrology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand 123 Rheumatol Int (2013) 33:1461–1467 DOI 10.1007/s00296-012-2537-7