The interactive effect of improvement of vitamin D status and VDR FokI variants on oxidative stress in type 2 diabetic subjects: a randomized controlled trial
Background/Objectives:The objectives were to evaluate the effects of improvement of vitamin D status on biomarkers of oxidative stress (OS) in type 2 diabetic (T2D) subjects and whether vitamin D receptor (VDR)-FokI polymorphisms could modulate the response to vitamin D3 intake.Subjects/Methods:Subjects with T2D were allocated to one of the two groups to receive either plain doogh (PD; containing 150 mg calcium and no vitamin D/250 ml, n1=50) or vitamin D3-fortified doogh (FD; containing 500 IU/250 ml, n1=50) twice a day for 12 weeks. Outcomes were changes in serum 25-hydroxyvitamin D (25(OH)D), superoxide dismutase, glutathione (GSH), total antioxidant capacity (TAC) and malondialdehyde (MDA). VDR genotypes in 140 T2D subjects in FD were determined by FokI restriction enzyme.Results:After 12 weeks, serum 25(OH)D increased significantly in FD (from 38.5±202.2 to 72.0±23.5, P<0.001) as compared with PD (from 38.8±22.8 to 33.4±22.8, P=0.28). Comparisons between FD and PD revealed significant differences in changes of serum MDA (−0.54±0.82 μmol/l vs +0.17±1 μmol/l, P<0.001), GSH (+8.4±40.1 ng/l vs −13.1±29.4 ng/l, P=0.002) and TAC (+0.14±0.43 mmol/l  vs +0.02±0.45 mmol/l bovine serum albumin equivalent, P=0.03). Although there was no significant association between FokI genotypes and OS biomarkers, ff variant subgroup showed the weakest response to vitamin D.Conclusions:Improvement of vitamin D status via daily intake of FD ameliorates OS biomarkers in T2D subjects and the interactive effect of FokI genotypes cannot be ruled out.