The predictive factors of low serum 25-hydroxyvitamin D and vitamin D deficiency in patients with systemic lupus erythematosus.
Rheumatol Int. 2012 Nov 22.
Sumethkul K, Boonyaratavej S, Kitumnuaypong T, Angthararuk S, Cheewasat P, Manadee N, Sumethkul V.
Rheumatology Unit, Department of Medicine, Rajavithi Hospital, 2 Rajavithi Road, Bangkok, 10400, Thailand, ckittiwan at hotmail.com.
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, ≥3 but no LN and ≥3 with LN. Important baseline characteristics were collected. 25(OH) D was measured by high performance liquid chromatography (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 multiple 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 insufficiency was found in 93 and 86 % of LN with proteinuria ≥ 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 significant predictor of vitamin D deficiency in SLE patients.
There are many ways of maintining or increasing vitamin D levels in blood even when kidneys are not functioning well.