Modulatory Properties of Vitamin D in Type 2 Diabetic Patients: A Focus on Inflammation and Dyslipidemia

Gender-specific association between circulating 25-hydroxyvitamin D levels and diabetic retinopathy in patients with type 2 diabetes mellitus

Background

Diabetic retinopathy (DR), one of the most common microvascular complications of diabetes mellitus (DM), remains to be a major driver of vision loss worldwide. Vitamin D has been reported to be involved in DR pathogenesis, but results have been inconsistent. We aimed to explore the relationship between blood 25-hydroxyvitamin D, 25(OH)D, level and the risk of DR in patients with type 2 diabetes (T2DM).

Methods

A total of 535 adults with T2DM from our department were included. Demographic information, biochemical data, 25(OH)D, and sex hormones were collected. Fundus photography was performed to determine the presence of DR. Participants were grouped into the DR group and the non-DR (NDR) group according to the fundus examinations and four groups based on serum 25(OH)D levels as follows: normal, insufficient, deficient, and severely deficient. Multivariate logistic regression analysis was used to evaluate the association between 25(OH)D and risk of DR.

Results

Males but not females with DR had significantly decreased levels of 25(OH)D (16.4 ± 5.6 ng/ml vs. 21.0 ± 5.0 ng/ml, P = 0.001) and increased proportion of severe 25(OH)D deficiency (14.8% vs. 6.7%, P = 0.022) compared to those without DR. Likewise, there was a gradually increasing percentage of DR with the reduction of 25(OH)D levels only in males (35.7%, 44.4%, 53.2%, 70.3%, P = 0.022). Intriguingly, total testosterone (TT) levels decreased markedly in males with DR (12.9 ± 5.2 nmol/L vs. 14.2 ± 5.5 nmol/L, P = 0.035) compared to their counterparts and correlated positively with 25(OH)D (β = 0.161, P = 0.007), which did not occur in females. After multivariate adjustment, we observed a significant inverse association between serum 25(OH)D and the occurrence of DR in males, showing that the adjusted ORs (AORs) and 95% confidence interval for DR were 0.233 (0.070-0.779) in the normal group, 0.280 (0.103-0.756) in the insufficient group, and 0.477 (0.196-1.164) in the deficiency group with the severely deficient group as a reference (P-trend = 0.003). However, such a significant association was not observed in females (P-trend = 0.137).

Conclusion

We concluded a gender-specific relationship between serum 25(OH)D and the incidence of DR in T2DM, supported by a significant inverse association between serum 25(OH)D and DR only in males, which could be mediated by a marked reduction in TT levels.

Exploring the anti-inflammatory potential of vitamin D in cardiometabolic diseases

The prevalence of cardiometabolic diseases is rising, and this is fuelled by inflammation, which tends to be worse in individuals with vitamin D (VD) deficiency. While non-steroidal anti-inflammatory interventions are available, they present with coagulation events. Hence, alternative therapy in the form of VD supplements is gaining research interest. This study reviewed the effect of VD supplementation on inflammation, focusing on nuclear factor kappa-beta (NF-κβ), tumour necrosis factor-alpha (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) across different cardiometabolic disease. Thirty-seven studies, 16 rodent models and 21 clinical studies were evaluated. The study considered evidence from rodent models to understand the effect of VD on these markers of inflammation and its translatability to clinical studies. While the potential benefits of VD were notable in rodents, these effects were less consistent in clinical studies. Notably, rodent models showed a more pronounced impact of VD in reducing NF-κβ and TNF-α; however, clinical trials reported conflicting findings. Furthermore, the VD was important in reducing MCP-1 across different rodent models; this was partially demonstrated in clinical trials. Based on these findings, VD modulates inflammation in cardiometabolic disease by inhibiting the activation of NF-κβ and suppressing the production of TNF-α and MCP-1. Although VD has some possible benefits in rodent models, the translatability of these findings in clinical trials is limited. Hence, the presented evidence in this study calls for further randomised controlled trials to assess the effect of VD on inflammation in patients living with different conditions as a therapy to curb the inflammation and the risk thereof. Future trials should also focus on exploring the VD dose-response, optimal dose, and duration of VD intervention among these patients that may offer optimal benefits on inflammation.

Oxidative Stress, Glutathione Insufficiency, and Inflammatory Pathways in Type 2 Diabetes Mellitus: Implications for Therapeutic Interventions

Type 2 diabetes mellitus (T2DM) is significantly associated with oxidative stress, resulting from the imbalance between reactive oxygen species (ROS) production and antioxidant defenses. This imbalance contributes to insulin resistance, β-cell dysfunction, and complications in organs like the vasculature and nervous system. Glutathione (GSH), a major antioxidant, is crucial for neutralizing ROS, but GSH levels are notably low in T2DM, exacerbating oxidative stress and inflammation. Elevated interleukin-6 (IL-6) levels further intensify inflammation and oxidative stress, disrupting insulin signaling and worsening complications such as nephropathy, retinopathy, and neuropathy. While lifestyle modifications and antioxidant supplementation are current approaches for managing oxidative stress, their effectiveness in preventing complications remains under study. Recent investigations suggest that GSH and Vitamin D3 supplementation may offer dual-action benefits, as Vitamin D3 not only has anti-inflammatory properties but also promotes GSH synthesis. This dual action helps mitigate both oxidative stress and inflammation, addressing key pathological features of T2DM. This review highlights the complex interactions between oxidative stress, GSH insufficiency, and IL-6, and emphasizes the potential of targeted therapies to improve the management and outcomes of T2DM.

Sulfation pathways in the maintenance of functional beta-cell mass and implications for diabetes

Diabetes Type 1 and Type 2 are widely occurring diseases. In spite of a vast amount of biomedical literature about diabetic processes in general, links to certain biological processes are only becoming evident these days. One such area of biology is the sulfation of small molecules, such as steroid hormones or metabolites from the gastrointestinal tract, as well as larger biomolecules, such as proteins and proteoglycans. Thus, modulating the physicochemical propensities of the different sulfate acceptors, resulting in enhanced solubility, expedited circulatory transit, or enhanced macromolecular interaction. This review lists evidence for the involvement of sulfation pathways in the maintenance of functional pancreatic beta-cell mass and the implications for diabetes, grouped into various classes of sulfated biomolecule. Complex heparan sulfates might play a role in the development and maintenance of beta-cells. The sulfolipids sulfatide and sulfo-cholesterol might contribute to beta-cell health. In beta-cells, there are only very few proteins with confirmed sulfation on some tyrosine residues, with the IRS4 molecule being one of them. Sulfated steroid hormones, such as estradiol-sulfate and vitamin-D-sulfate, may facilitate downstream steroid signaling in beta-cells, following de-sulfation. Indoxyl sulfate is a metabolite from the intestine, that causes kidney damage, contributing to diabetic kidney disease. Finally, from a technological perspective, there is heparan sulfate, heparin, and chondroitin sulfate, that all might be involved in next-generation beta-cell transplantation. Sulfation pathways may play a role in pancreatic beta-cells through multiple mechanisms. A more coherent understanding of sulfation pathways in diabetes will facilitate discussion and guide future research.

Association Between Decreased Serum Vitamin D Level and Dyslipidemia: A Cross-Sectional Study in Southern Taiwan

Purpose

Previous studies revealed an inconclusive association between dyslipidemia and decreased vitamin D levels. This study aims to investigate the association between dyslipidemia parameters and decreased serum vitamin D levels among the southern Taiwanese population during a health examination.

Patients and Methods

A retrospective cross-sectional study was conducted from January 2020 to December 2020, enrolling 2430 subjects in a southern Taiwanese medical center. We performed logistic regression to examine the association between lipid profiles and vitamin D insufficiency or deficiency.

Results

The prevalence of vitamin D sufficiency was higher in males (65.9%). Compared to individuals with total cholesterol (TC) < 200 mg/dL, those with TC ≥ 200 mg/dL exhibited vitamin D insufficiency or deficiency (OR, 1.46; 95% confidence intervals (CI), 1.10-1.94) after adjustment for age, gender, waist circumference (WC), fasting blood glucose, and uric acid levels. Compared to triglyceride (TG) levels of <150 mg/dL, TG levels ≥ 150 mg/dL had a higher association with vitamin D insufficiency or deficiency (OR, 1.48; 95% CI, 1.17-1.86) after adjustment for the same covariates. Post-gender stratification, we found female individuals with TC ≥ 200 mg/dL had a significantly higher association with vitamin D insufficiency or deficiency (OR, 2.11; 95% CI, 1.36-3.27), whereas TG ≥ 150 mg/dL in males exhibited a significantly higher association with vitamin D insufficiency or deficiency (OR, 1.70; 95% CI, 1.29-2.24) after adjustment for the same covariates.

Conclusion

The study revealed a negative association between decreased serum vitamin D levels and TC and TG levels. However, no significant association was observed with low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C). Further studies are needed to understand the mechanism.

Folic acid supplementation on inflammation and homocysteine in type 2 diabetes mellitus: systematic review and meta-analysis of randomized controlled trials

BACKGROUND

The beneficial effects of folate have been observed under different conditions, but the available evidence on inflammation and reduction of cardiovascular disease (CVD) in type 2 diabetes mellitus (T2DM) is limited. The study aimed to explore the effects of folate on inflammation and homocysteine amongst individuals with T2DM.

METHODS

PubMed, Scopus, and Cochrane Library were used to search for evidence. A random-effect model meta-analysis through Review Manager (version 5.4) and metaHun was performed. Results were reported as standardized mean differences (SMD) and 95% confidence intervals graphically using forest and funnel plots.

RESULTS

Data from 9 trials with 426 patients living with T2DM were analyzed. Folic acid supplementation significantly revealed a large effect size on homocysteine levels compared to placebo, SMD = -1.53, 95%CI (-2.14,-0.93), p < 0.05. Additionally, we observed a medium marginal effect size on C-reactive protein (SMD = -0.68, 95%CI (-1.34, -0.01), p = 0.05). However, no significant effect on tumor necrosis factor-α (SMD = -0.86, 95%CI (-2.65, 0.93), p = 0.34), and interleukin-6 (SMD = -0.04, 95%CI (-1.08, 1.01), p = 0.95) was observed.

CONCLUSION

Evidence analyzed in this study suggests that folic acid supplementation in T2DM reduces homocysteine and may mitigate CVDs. However, its effect on inflammation is inconclusive.

Vitamin D and Dyslipidemia: Is There Really a Link? A Narrative Review

Nowadays, the interest in the extraskeletal effects of vitamin D is growing. In the literature, its several possible actions have been confirmed. Vitamin D seems to have a regulatory role in many different fields-inflammation, immunity, and the endocrine system-and many studies would demonstrate a possible correlation between vitamin D and cardiovascular disease. In this paper, we deepened the relationship between vitamin D and dyslipidemia by reviewing the available literature. The results are not entirely clear-cut: on the one hand, numerous observational studies suggest a link between higher serum vitamin D levels and a beneficial lipid profile, while on the other hand, interventional studies do not demonstrate a significant effect. Understanding the possible relationship between vitamin D and dyslipidemia may represent a turning point: another link between vitamin D and the cardiovascular system.

Effects of vitamin family members on insulin resistance and diabetes complications

The following letter to the editor highlights the article "Effects of vitamin D supplementation on glucose and lipid metabolism in patients with type 2 diabetes mellitus and risk factors for insulin resistance" in World J Diabetes 2023 Oct 15; 14 (10): 1514-1523. It is necessary to explore the role of vitamin family members in insulin resistance and diabetes complications.