Vitamin C may have similar beneficial effects to Gemfibrozil on serum high-density lipoprotein-cholesterol in type 2 diabetic patients

Research Progress on the Relationship between Vitamins and Diabetes: Systematic Review

Diabetes is a serious chronic metabolic disease that causes complications over time, bringing serious public health challenges that affect different countries across the world. The current clinical drugs for diabetes may lead to adverse effects such as hypoglycemia and liver and abdominal distension and pain, which prompt people to explore new treatments for diabetes without side effects. The research objective of this review article is to systematically review studies on vitamins and diabetes and to explain their possible mechanism of action, as well as to assess the role of vitamins as drugs for the prevention and treatment of diabetes. To achieve our objective, we searched scientific databases in PubMed Central, Medline databases and Web of Science for articles, using "vitamin" and "diabetes" as key words. The results of numerous scientific investigations revealed that vitamin levels were decreased in humans and animals with diabetes, and vitamins show promise for the prevention and/or control of diabetes through anti-inflammation, antioxidation and the regulation of lipid metabolism. However, a few studies showed that vitamins had no positive effect on the development of diabetes. Currently, studies on vitamins in the treatment of diabetes are still very limited, and there are no clinical data to clarify the dose-effect relationship between vitamins and diabetes; therefore, vitamins are not recommended as routine drugs for the treatment of diabetes. However, we still emphasize the great potential of vitamins in the prevention and treatment of diabetes, and higher quality studies are needed in the future to reveal the role of vitamins in the development of diabetes.

The effects of vitamin C supplementation on glycemic control in patients with type 2 diabetes: A systematic review and meta-analysis

BACKGROUND AND AIM

It has been suggested that taking vitamin C supplements may improve glycemic control in patients with type 2 diabetes mellitus (T2DM). However, there has not been a thorough evaluation of the actual impact or certainty of the findings. This systematic review and meta-analysis was conducted to determine the effect of vitamin C supplementation on glycemic profile in T2DM patients.

METHODS

A systematic search was performed across online databases including Scopus, Web of Science, and PubMed/Medline to identify relevant randomized controlled trials (RCTs) published until July 2022. A random-effects model was applied for the meta-analysis.

RESULTS

The present meta-analysis included a total of 22 RCTs with 1447 patients diagnosed with T2DM.A pooled analysis revealed a significant decrease in levels of serum hemoglobin A1c (HbA1c), fasting insulin, and fasting blood glucose (FBG) in vitamin C-treated T2DM patients compared with their untreated counterparts. The dose-response evaluation displayed a substantial linear association between the intervention duration and changes in serum HbA1c levels. However, the analysis did not demonstrate any significant effect of vitamin C on serum values of homeostasis model assessment of insulin resistance(HOMA-IR) in diabetic patients. Subgroup analyses indicated that high-dose vitamin C administration (≥1000 mg/d) considerably decreased serum HOMA-IR levels.

CONCLUSION

These findings suggest that long-term (≥12 weeks) and high-dose vitamin C supplementation (≥1000 mg/d) may ameliorate glycemic profile in T2DM patients. However, additional high-quality RCTs are necessary to validate these results.

Reactive oxygen species in exercise and insulin resistance: Working towards personalized antioxidant treatment

Reactive oxygen species (ROS) are well known for their role in insulin resistance and the development of cardiometabolic disease including type 2 diabetes mellitus (T2D). Conversely, evidence supports the notion that ROS are a necessary component for glucose cell transport and adaptation to physiological stress including exercise and muscle contraction. Although genetic rodent models and cell culture studies indicate antioxidant treatment to be an effective strategy for targeting ROS to promote health, human findings are largely inconsistent. In this review we discuss human research that has investigated antioxidant treatment and glycemic control in the context of health (healthy individuals and during exercise) and disease (insulin resistance and T2D). We have identified key factors that are likely to influence the effectiveness of antioxidant treatment: 1) the context of treatment including whether oxidative distress or eustress is present (e.g., hyperglycemia/lipidaemia or during exercise and muscle contraction); 2) whether specific endogenous antioxidant deficiencies are identified (redox screening); 3) whether antioxidant treatment is specifically designed to target and restore identified deficiencies (antioxidant specificity); 4) and the bioavailability and bioactivity of the antioxidant which are influenced by treatment dose, duration, and method of administration. The majority of human research has failed to account for these factors, limiting their ability to robustly test the effectiveness of antioxidants for health promotion and disease prevention. We propose that a modern "redox screening" and "personalized antioxidant treatment" approach is required to robustly explore redox regulation of human physiology and to elicit more effective antioxidant treatment in humans.

Does vitamin C supplementation exert profitable effects on serum lipid profile in patients with type 2 diabetes? A systematic review and dose-response meta-analysis

Previous studies have reported that vitamin C supplementation may decrease lipid profile in patients with type 2 diabetes mellitus (T2DM). This systematic review and meta-analysis evaluated the influence of vitamin C supplementation on lipid profile in patients with T2DM. Studies examining the effects of vitamin C supplementation on lipid profile in patients with T2DM, published up to November 2020, were identified through PubMed, SCOPUS, and Embase databases. 15 studies, including 872 participants, were included and analyzed using a random-effects model to calculate weighted mean differences (WMDs) with 95% confidence intervals (CI). Findings from 15 studies indicated that vitamin C supplementation significantly decreased Triglyceride (TG) (WMD: -16.48 mg/dl, 95% CI (-31.89, -1.08), P < 0.001) and total cholesterol (TC) (WMD: -13.00 mg/dl, 95% CI (-23.10, -2.91), P < 0.001) in patients with T2DM. However, vitamin C supplementation failed to improve LDL and HDL. The meta-regression analysis suggested that lipid profile improvement was affected by duration of vitamin C treatment. Dose-response analysis showed that vitamin C supplementation changed LDL significantly based on vitamin C dose. According to our findings, vitamin C supplementation significantly improved lipid profile via decreases in TG and TC. However, vitamin C failed to affect LDL and HDL in diabetic populations. It appears that vitamin C supplementation is more beneficial to lipid profile in long-term vs. short term interventions.

Effects of Vitamin C Supplementation on Glycemic Control and Cardiovascular Risk Factors in People With Type 2 Diabetes: A GRADE-Assessed Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

Evidence suggests that vitamin C supplementation could be a potential therapy in type 2 diabetes. However, its effectiveness and evidence quality require further evaluation.

PURPOSE

To investigate the efficacy of oral vitamin C supplementation in improving glycemic control, cardiovascular risk factors, and oxidative stress in people with type 2 diabetes.

DATA SOURCES

Databases (PubMed, Embase, Scopus, Cochrane Library) and clinical trial registries were searched for randomized controlled trials up to 8 September 2020.

STUDY SELECTION

Trials in adults with type 2 diabetes were included. Trials were excluded if supplements were not exclusive to vitamin C and if <2 weeks in duration.

DATA EXTRACTION

Primary outcomes were HbA_1c, glucose, cholesterol, triglycerides, and blood pressure (BP). Data were extracted for changes in outcomes between vitamin C and control groups. Evidence certainty was assessed using Grading of Recommendations, Assessment, Development, and Evaluation methods.

DATA SYNTHESIS

Twenty-eight studies (N = 1,574 participants) were included in the review. Outcomes that changed to a statistically and clinically significant extent with vitamin C were systolic BP (mean difference -6.27 [95% CI -9.60, -2.96] mmHg; P = 0.0002), with moderate evidence certainty, and HbA_1c (-0.54% [-0.90, -0.17]; P = 0.004) and diastolic BP (-3.77 [-6.13, -1.42] mmHg; P = 0.002) with very low evidence certainty.

LIMITATIONS

Studies were predominantly short term (<6 months) with a small number of participants (n < 100).

CONCLUSIONS

While evidence from short-term studies suggests that vitamin C supplementation may improve glycemic control and BP in people with type 2 diabetes, vitamin C supplementation cannot currently be recommended as a therapy until larger, long-term, and high-quality trials confirm these findings.

Multiple Effects of Ascorbic Acid against Chronic Diseases: Updated Evidence from Preclinical and Clinical Studies

Severe disease commonly manifests as a systemic inflammatory process. Inflammation is associated withthe enhanced production of reactive oxygen and nitrogen species and with a marked reduction in the plasma concentrations of protective antioxidant molecules. This imbalance gives rise to oxidative stress, which is greater in patients with more severe conditions such as sepsis, cancer, cardiovascular disease, acute respiratory distress syndrome, and burns. In these patients, oxidative stress can trigger cell, tissue, and organ damage, thus increasing morbidity and mortality. Ascorbic acid (ASC) is a key nutrient thatserves as an antioxidant and a cofactor for numerous enzymatic reactions. However, humans, unlike most mammals, are unable to synthesize it. Consequently, ASC must be obtained through dietary sources, especially fresh fruit and vegetables. The value of administering exogenous micronutrients, to reestablish antioxidant concentrations in patients with severe disease, has been recognized for decades. Despite the suggestion that ASC supplementation may reduce oxidative stress and prevent several chronic conditions, few large, randomized clinical trials have tested it in patients with severe illness. This article reviews the recent literature on the pharmacological profile of ASC and the role of its supplementation in critically ill patients.

Arachidonic Acid Metabolism and Kidney Inflammation

As a major component of cell membrane lipids, Arachidonic acid (AA), being a major component of the cell membrane lipid content, is mainly metabolized by three kinds of enzymes: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) enzymes. Based on these three metabolic pathways, AA could be converted into various metabolites that trigger different inflammatory responses. In the kidney, prostaglandins (PG), thromboxane (Tx), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are the major metabolites generated from AA. An increased level of prostaglandins (PGs), TxA₂ and leukotriene B4 (LTB₄) results in inflammatory damage to the kidney. Moreover, the LTB₄-leukotriene B4 receptor 1 (BLT1) axis participates in the acute kidney injury via mediating the recruitment of renal neutrophils. In addition, AA can regulate renal ion transport through 19-hydroxystilbenetetraenoic acid (19-HETE) and 20-HETE, both of which are produced by cytochrome P450 monooxygenase. Epoxyeicosatrienoic acids (EETs) generated by the CYP450 enzyme also plays a paramount role in the kidney damage during the inflammation process. For example, 14 and 15-EET mitigated ischemia/reperfusion-caused renal tubular epithelial cell damage. Many drug candidates that target the AA metabolism pathways are being developed to treat kidney inflammation. These observations support an extraordinary interest in a wide range of studies on drug interventions aiming to control AA metabolism and kidney inflammation.

Vitamin supplements in type 2 diabetes mellitus management: A review

Type 2 diabetes mellitus (T2DM) is a major public health challenge that affects countries across the world. The use of pharmacological therapy is often limited in some patients due to a loss of effect over time or development of adverse effects such as weight gain or hypoglycaemia. This has prompted searches into the role of non-pharmacological therapies in T2DM. The availability and use of vitamin supplements in developed countries have increased significantly and there is evidence that certain vitamins may have roles in the management of T2DM. This review examines the literature assessing the use of vitamins A, C, E, D, K and the B group vitamins (B1, B3, B7, B6, B9, B12) in the management of T2DM. No clear evidence supporting the beneficial role of any specific vitamin in the treatment of T2DM was found. Thus, it is recommended that until further studies are conducted to clarify the role of such vitamins in T2DM management, they should not be routinely recommended in clinical practice.

Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials

Randomised controlled trials (RCTs) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation. We conducted a systematic review and meta-analysis of RCTs testing the effect of vitamin C administration on glucose, HbA1c and insulin concentrations. Four databases (PubMed, Embase, Scopus and Cochrane Library) were used to retrieve RCTs published from inception until April 2016 and testing the effects of vitamin C in adult participants. The screening of 2008 articles yielded 22 eligible studies (937 participants). Overall, vitamin C did not modify glucose, HbA1c and insulin concentrations. However, subgroup analyses showed that vitamin C significantly reduced glucose concentrations (-0.44 mmol/l, 95% CI: -0.81, -0.07, P=0.01) in patients with type 2 diabetes and in interventions with a duration greater than 30 days (-0.53%, 95% CI: -0.79, -0.10, P=0.02). Vitamin C administration had greater effects on fasting (-13.63 pmol/l, 95% CI: -22.73, -4.54, P<0.01) compared to postprandial insulin concentration. Meta-regression analyses showed that age was a modifier of the effect of vitamin C on insulin concentration. Furthermore, the effect size was associated with baseline BMI and plasma glucose levels, and with the duration of the intervention. In conclusion, greater reduction in glucose concentrations observed in patients with diabetes, older individuals and with more prolonged supplementation. Personalised interventions with vitamin C may represent a feasible future strategy to enhance benefits and efficacy of interventions. Nevertheless, results need to be interpreted cautiously due to limitations in the primary studies analysed.

Obesity, cardiovascular disease, and role of vitamin C on inflammation: a review of facts and underlying mechanisms

Obesity means the accumulation of excessive fat that may interfere with the maintenance of optimal state of health. Obesity causes cardiac and vascular disease through well-known mediators such as hypertension, type-2 diabetes mellitus, and dyslipidemia, but there are evidences for other mediators such as chronic inflammation, oxidative stress, and thrombosis. The decreased levels of antioxidants factors and nitric oxide predispose to further cardiovascular adverse events. To reduce the risks, antioxidants can help by neutralizing the free radicals and protecting from damage by donating electrons. Having the capacity, vitamin C protects from oxidative stress, prevention of non-enzymatic glycosylation of proteins, and enhances arterial dilation through its effect on nitric oxide release. It also decreases lipid peroxidation, and alleviates inflammation. The anti-inflammatory property of vitamin C could be attributed to ability to modulate the NF-_kB DNA binding activity and down-regulation in the hepatic mRNA expression for the interleukins and tumor factors.

Application research on PPARα-transgenic mice in preclinical safety evaluation of gemfibrozil

To explore the feasibility of peroxisome proliferator-activated receptor (PPAR)α transgenic mice applying in preclinical safety evaluation for peroxisome proliferators (PPs). Both PPARα transgenic mice and C57BL/6J mice were assigned as treated groups (PT and CT groups) and control groups (PC and CC groups). Gemfibrozil was administered into treated groups for 4 weeks. Body weight, blood biochemistry, enzyme activity and histological examinations were performed at scheduled time. The results showed that significant hypolipidaemic effects were induced in the treated groups after gemfibrozil treatment whereas the changes of non-esterified fatty acid and high density lipoproteincholesterol were different between the two treated groups. All the enzyme activities examined increased significantly in PT and CT groups except catalase which displayed no obvious change in the PT group. Pathology results showed a significant increase of the liver weight and the liver weight ratio in the CT group while no obvious changes were observed in the PT group. Hypertrophy of hepatocytes was discovered in CT and PT groups in histological examination, while the extent and incidence of hepatocyte hypertrophy in the CT group were higher than those in the PT group. The data suggest that PPARα transgenic mice could serve as a useful tool for preclinical safety assessment of PP drugs.

Danhong Huayu Koufuye combined with metformin attenuated diabetic retinopathy in Zucker diabetic fatty rats

AIM

To evaluate effects of Danhong Huayu Koufuye (DHK, a Chinese medicinal formulae) alone or combined with metformin on diabetic retinopathy (DR) in Zucker diabetic fatty (ZDF) rats, an animal model of obese type-2 diabetes, and then to investigate the mechanisms.

METHODS

ZDF (fa/fa) rats were administered with vehicle (distilled water), metformin, DHK, and DHK plus metformin. Electrophysiological and histological analysis were applied to evaluated effects of DHK alone or combined with metformin on DR. The levels of fasting blood glucose (FBG) and glycosylated hemoglobin (HbA1c) in blood were measured to evaluate the antihyperglycemic activity of DHK. Furthermore, levels of nitric oxide (NO), malondialdehyde (MDA) and activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) in serum were measured to study effects of DHK on oxidative stress in ZDF rats. In addition, body weight, lipidic indexes and insulin level were also assessed.

RESULTS

DHK combined with metformin significantly reversed the prolongation of latency times of flash electroretinogram (FERG) and oscillatory potentials (OPs) in diabetic rats. Furthermore, DHK alone or combined with metformin showed a remarkable suppression of retinal neovascularization and amelioration of retinal internal limiting membrane morphology. Moreover, DHK alone or plus metformin reduced FBG (P<0.05), HbA1c (P<0.01) and MDA (P<0.01) levels in diabetic rats. In addition, reductions in levels of triglycerides (TG) (P<0.01) and low density lipoprotein cholesterol (LDL-c) (P<0.01 and P<0.05, respectively) were also observed in diabetic rats treated with DHK alone or plus metformin.

CONCLUSION

DHK in combination with metformin had a preventive and therapeutic effect on DR in type-2 diabetic rats, and the possible mechanisms may be alleviating hyperglycemia, reducing oxidative stress and improving lipid metabolism.

Effect of vitamin C on inflammation and metabolic markers in hypertensive and/or diabetic obese adults: a randomized controlled trial

BACKGROUND

Obesity is well associated as being an interfering factor in metabolic diseases such as hypertension and diabetes by increasing the secretion of proinflammatory markers from adipose tissue. Having healthy effects, vitamin C could work as an anti-inflammatory agent through its antioxidant capacity.

REGISTRATION

REGISTRATION NUMBER

FPSK_Mac [13]04.

OBJECTIVE

The aim of the study reported here was to identify the effect of vitamin C on reducing the levels of inflammatory markers in hypertensive and/or diabetic obese adults.

SUBJECTS AND METHODS

Sixty-four obese patients, who were hypertensive and/or diabetic and had high levels of inflammatory markers, from primary health care centers in Gaza City, Palestine, were enrolled into one of two groups in an open-label, parallel, randomized controlled trial. A total of 33 patients were randomized into a control group and 31 patients were randomized into an experimental group. The experimental group was treated with 500 mg vitamin C twice a day.

RESULTS

In the experimental group, vitamin C significantly reduced the levels of high-sensitivity C-reactive protein (hs-CRP), interleukin 6 (IL-6), fasting blood glucose (FBG), and triglyceride (TG) after 8 weeks of treatment (overall: P<0.001); no changes appeared in total cholesterol (TC). In the control group, there were significant reductions in FBG and TG (P=0.001 and P=0.026, respectively), and no changes in hs-CRP, IL-6, or TC. On comparing the changes in the experimental group with those in the control group at the endpoint, vitamin C was found to have achieved clinical significance in treating effectiveness for reducing hs-CRP, IL-6, and FBG levels (P=0.01, P=0.001, and P<0.001, respectively), but no significant changes in TC or TG were found.

CONCLUSION

Vitamin C (500 mg twice daily) has potential effects in alleviating inflammatory status by reducing hs-CRP, IL-6, and FBG in hypertensive and/or diabetic obese patients.