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Background Iron and vitamin D (VD) is essential to health. Previous studies have shown that iron homeostasis has a potential effect on VD metabolism, but the mechanism is not fully understood. Objectives To explore the relationship between VD metabolism and iron metabolism, as well as the regulatory mechanism of iron on VD metabolism. Methods 40 male rats were fed adaptively for 7 days and randomly divided into control (C, n = 6 normal diet) group and model (M, n = 24 iron deficient diet) by simple randomization, the latter was used to establish iron deficiency anemia (IDA) model. After 6 weeks of feeding, the M group was randomly divided into: iron deficiency group (DFe), low iron group (LFe), medium iron group (MFe) and high iron group (HFe) by block randomization. Different doses of iron dextran (based on iron content (100 g·bw·d)): 0, 1.1, 3.3 and 9.9 mg) were given respectively. After 4 weeks, the rats were anesthetized with 8% chloral hydrate, Blood (collected from the abdominal aorta), liver and kidney tissues were collected. The serum and tissues were separately packed and frozen at -80℃ for testing. Results The results showed that the levels of hemoglobin (Hb), red blood cell (RBC), serum iron (SI), liver iron, and kidney iron in DFe group were lower than those in the other four groups, while the levels of total iron-binding capacity (TIBC), transferrin (TF) and transferrin receptor (Tfr) in DFe group were higher than those in other groups; The serum levels of 25-(OH)D3 and 1,25-(OH)2D3 in DFe group were significantly lower than those in C group (P < 0.05). The correlation analysis showed that the levels of 25-(OH)D3 and 1,25-(OH)2D3 were negatively correlated with TIBC, TF and Tfr no correlation with SI. Western blotting, immunofluorescence, and q-PCR results showed that compared with C group, the protein and gene expressions of CYP2R1, CYP27A1, and CYP24A1 in DFe group were down-regulated, and the expression of CYP27B1 protein and gene was up-regulated in DFe group. Conclusion Iron may be involved in the metabolism of VD3 by regulating the expression of VD3 hydroxylase, suggesting that appropriate iron supplementation might promote the activation of VD3.

Object Vitamin D (VD) deficiency has been reported in patients with ulcerative colitis (UC), and polymorphism in the gene encoding the vitamin D binding protein (DBP) can affect the characteristics of DBP, thus affecting the level and function of VD in vivo . Previous studies have rarely reported on the potential relationship between DBP polymorphisms and UC. To investigate the associations between genetic variants in DBP genes and UC susceptibility in the Han Chinese population, in order to discern whether any differences exist between this population and those of other countries.Methods In this case-control study, the genotyping of DBP rs4588 and rs7041 polymorphisms was conducted using polymerase chain reaction (PCR)-ligase detection reactions, and the rs4588 and rs7041 genotypes were detected by PCR-restriction fragment length polymorphism.Results In our case-control cohort, no significant difference was observed in the UC risk for either of the two SNPs (rs4588 and rs7401) in the DBP genes ( P > 0.05). No association between UC susceptibility and the DBP gene haplotypes was found either.Conclusions Our results suggest that the two SNPs (rs4588 and rs7401) in the DBP genes may have no correlation with susceptibility to UC in the Chinese Han population. But interestingly, haplotype GC, which contains the rs4588 and rs7041 variants in the DBP gene, may affect the level of oxidative stress in UC patients, especially the level of MDA.