The Association of Serum Vitamin D Deficiency and Metabolic Risk Factors in Chinese Adults with Prediabetes: A Cross-Sectional Study

Serum 25-hydroxyvitamin D might be negatively associated with hyperuricemia in U.S. adults: an analysis of the National Health and Nutrition Examination Survey 2007-2014

PURPOSE

The results of previous studies on the relationship between serum 25-hydroxyvitamin D [25(OH)D] and hyperuricemia are controversial. We hypothesized that serum 25(OH)D concentrations of U.S. adults would negatively correlate with the risk of hyperuricemia.

METHOD

Data came from the National Health and Nutrition Examination Survey 2007-2014 were used, after excluding those who met at least one of the exclusion criteria, a total of 9096 male individuals and 9500 female individuals aged 18 years or older were included. Binary logistic regression analysis and restricted cubic spline with fully adjusted confounding factors were applied to evaluate the association between serum 25(OH)D and hyperuricemia. We further performed stratified analysis and sensitivity analysis to minimize the influence of gender, metabolic syndrome, obesity and renal dysfunction on the above association.

RESULTS

We found a negative correlation between serum 25(OH)D and hyperuricemia. In the binary logistic regression analysis, compared with the highest serum 25(OH)D quartile [Q4: 25(OH)D > 77.10 nmol/L] group, the odds ratios (95% confidence intervals) in the lowest quartile [Q1: 25(OH)D ≤ 43.20 nmol/L] was 1.46 (1.22-1.75) in the fully adjusted model. Restricted cubic spline analysis showed L-shaped and non-linear relationships between 25(OH)D and hyperuricemia. In sensitivity analysis, after restricting to participants without significant renal dysfunction and obesity, the above association remained significant. After restricting to participants who were diagnosed as metabolic syndrome, above association remained significant in the fully adjusted model. In stratified analysis by gender, the association remained significant among males and females.

CONCLUSIONS

Serum 25(OH)D might be inversely associated with hyperuricemia in general U.S. adults. From our study, for people with unexplained hyperuricemia, screening for serum Vitamin D concentration might be necessary.

Vitamin D signaling maintains intestinal innate immunity and gut microbiota: potential intervention for metabolic syndrome and NAFLD

A lack of sunlight exposure, residence in the northern latitudes, and dietary vitamin D insufficiency are coprevalent with metabolic syndrome (MetS), Type 2 diabetes (T2D), and nonalcoholic fatty liver diseases (NAFLD), implying a potential causality and underlying mechanism. Whether vitamin D supplementation or treatment can improve these disorders is controversial, in part, because of the absence of large-scale trials. Experimental investigations, on the other hand, have uncovered novel biological functions of vitamin D in development, tumor suppression, and immune regulation, far beyond its original role as a vitamin that maintained calcium homeostasis. While the large intestine harbors massive numbers of microbes, the small intestine has a minimal quantity of bacteria, indicating the existence of a gating system located in the distal region of the small intestine that may restrain bacterial translocation to the small intestine. Vitamin D receptor (VDR) was found to be highly expressed at the distal region of small intestine, where the vitamin D signaling promotes innate immunity, including the expression of α-defensins by Paneth cells, and maintains the intestinal tight junctions. Thus, a new hypothesis is emerging, indicating that vitamin D deficiency may impair the intestinal innate immunity, including downregulation of Paneth cell defensins, leading to bacterial translocation, endotoxemia, systemic inflammation, insulin resistance, and hepatic steatosis. Here, we review the studies for vitamin D for innate immunity and metabolic homeostasis, and we outline the clinical trials of vitamin D for mitigating MetS, T2D, and NAFLD.

Association between vitamin D and prediabetes: A PRISMA-compliant meta-analysis

BACKGROUND

Previous studies showed conflicting results for associations between vitamin D and prediabetes. The study aimed to make a systematic review and meta-analysis for the association between vitamin D and prediabetes.

METHODS

We searched for articles identifying associations between vitamin D and prediabetes published in English until July 2019 in following databases (PubMed, Web of Science, EMBASE, Medline, Google Scholar, and Cochrane databases). Finally, we conducted these analyses (heterogeneities examination, meta-regression analyses, sensitivity analysis, and publication bias examination) using STATA 12.0 software (Stata Corporation, College Station, TX, USA). Q test and I were applied to examine heterogeneities between studies.

RESULTS

Twelve studies were finally included in the present study. The study included 4 studies to explore the association between serum levels of 25-hydroxy (OH) vitamin D and risks of prediabetes (including 3094 participants). Additionally, the present study included 8 studies (including 865 individuals with prediabetes treated with vitamin D supplementation and 715 patients treated with placebo) to assess differences in therapeutic effects between individuals with prediabetes treated with vitamin D supplementation and those treated with placebo. The present study showed no significant associations between low serum levels of 25(OH) vitamin D and high risk of prediabetes. Additionally, the study showed no significant differences in changes of hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), and homeostatic model assessment of insulin resistance (HOMA-IR) between individuals with prediabetes treated with vitamin D and those patients given placebo, whereas meta-analysis showed significantly greater changes in 2-hour oral glucose tolerance test (2HPG) in individuals with prediabetes treated with vitamin D, compared with individuals with prediabetes treated with placebo.

CONCLUSION

The study supported that low serum levels of 25(OH) vitamin D increased the risk of prediabetes. In addition, vitamin D supplementation improves impaired glucose tolerance in prediabetes. However, more large-scale clinical trials are essential to explore the association between vitamin D and prediabetes.