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Vitamin C and Diabetes

January 23, 2012 Written by JP    [Font too small?]

The pressing issue of type 2 diabetes recently took on an unexpected spokesman: Paula Deen. Ever since the highly publicized announcement of her illness and related drug endorsement, a hailstorm of negative and positive reactions has made its way to all forms of media. Instead of adding yet another voice to the chorus, I’ve decided to share some breaking information for Ms. Deen and other type-2 diabetics that may improve their health care prospects.

The simple addition of Vitamin C to conventional diabetes treatment can safely and significantly improve fasting, postmeal and long-term (HbA1c) blood sugar levels in adults with diabetes mellitus or DM. This finding was published in the December 28th edition of the journal Advances in Pharmacological Sciences. In the 12 week study, 500 mg of ascorbic acid (Vitamin C) was taken twice-daily along with the popular diabetes drug metformin. Another relatively obscure trial from March 2011 reports that a combination of purified fish oil (EPA) and Vitamin C effectively lowers blood sugar, LDL (“bad”) cholesterol and triglycerides, while elevating HDL (“good”) cholesterol. The latter study employed a daily dosage of 500 mg of EPA and 200 mg of Vitamin C.

Sadly, many physicians do not recommend therapeutic levels of Vitamin C to patients with DM. Their rationale is based on a general consensus that supplemental antioxidants don’t confer important changes to health outcomes in diabetics. But, it’s important to note that even conservative reviews of antioxidant therapy in DM tend to point out some benefits. For instance, a critical summary from February 2011 states that antioxidants, “can decrease lipid peroxidation, LDL-cholesterol particles oxidation and improve endothelial function and endothelial-dependent vasodilatation” – changes that lower the risk of cardiovascular disease. In addition, current studies reveal that adults with blood sugar disorders and related complications tend to have lower plasma Vitamin C than healthy adults. All of this research strongly suggests that improving Vitamin C levels via diet and/or supplementation addresses an underlying cause of diabetes and its comorbidities.

For those who prefer getting their Vitamin C partially or wholly from food, consider my top ten list of fruits and vegetables that contain the most Vitamin C: broccoli, Brussels sprouts, cabbage, cauliflower, kale, lemons, limes, mustard greens, red bell peppers and strawberries. Of the ten, I want to emphasize the value of eating more red bell peppers. A single serving provides upwards of 300% of the recommended daily value of Vitamin C. Peppers also contain a wealth of complementary antioxidants and phytochemicals which may yield additional protection for diabetics and just about everyone else. When selecting peppers, I recommend choosing the organic variety and opting for those that are kept under refrigeration. Conventionally grown bell peppers are on the Environmental Working Group’s “Dirty Dozen” list of produce containing pesticide residues. Refrigeration is important because unrefrigerated peppers demonstrate a precipitous decline in Vitamin C content.

Note: Please check out the “Comments & Updates” section of this blog – at the bottom of the page. You can find the latest research about this topic there!

To learn more about the studies referenced in today’s column, please click on the following links:

Study 1 – Supplementation of Vitamin C Reduces Blood Glucose and Improves (link)

Study 2 – Effects of Eicosapentaenoic Acid and Vitamin C on Glycemic Indices (link)

Study 3 – Antioxidants and Diabetes Mellitus: Review of the Evidence (link)

Study 4 – Serum Antioxidant Status Is Associated with Metabolic Syndrome (link)

Study 5 – Relationships Among Diabetic Retinopathy, Antioxidants and Glycemic (link)

Study 6 – Nutrition Data: Peppers, Sweet, Red, Raw (link)

Study 7 – Microbial Quality and Bioactive Constituents of Sweet Peppers from (link)

Study 8 – The Effects of Ripening Stage and Processing Systems on Vitamin C (link)

Study 9 – Characterization and Quantification of Antioxidant Constituents of (link)

Study 10 – Antioxidant Systems and Their Relationship with the Response of (link)

Vitamin C Works Synergistically with Metformin to Lower Blood Sugar

Source: Adv Pharmacol Sci. 2011; 2011: 195271. (link)

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Posted in Diabetes, Nutrition, Nutritional Supplements

10 Comments & Updates to “Vitamin C and Diabetes”

  1. Paul F. Says:

    Hi JP,
    I will share this valuable article with several diabetic friends that can benefit. This issue is very timely!
    I am sure many, many people, will love to implement this easy strategy,and attain good prevention for CVD.
    Thank you! God bless you!

  2. JP Says:

    Excellent, Paul! I’d love for you to spread the word. Information is power! 🙂

    God bless you too!

    Be well!


  3. JP Says:

    Update: Vitamin C supplementation may increase HDL (“good”) cholesterol in diabetics …


    J Res Pharm Pract. 2014 Jul;3(3):77-82.

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

    OBJECTIVE: Type 2 diabetes mellitus (DM-T2) is commonly associated with increased triglycerides (TG), low-density lipoprotein cholesterol (LDL-C) and low high-density lipoprotein cholesterol (HDL-C) levels. Fibrates like gemfibrozil are frequently used in diabetic patients to decrease TG and increase HDL-C levels. We compared the efficacy of Vitamin C, an antioxidant vitamin, with gemfibrozil on serum HDL-C in diabetic patients.

    METHODS: Type 2 diabetic patients, referred to our out-patient clinic were randomly divided into three groups. After 1 month of lifestyle and diet modifications, groups A, B, and C were prescribed 1000 mg Vitamin C, 600 mg gemfibrozil and combination of both, respectively. Before the study initiation and after 6(th) week of drug prescription, the blood samples were taken and analyzed for total cholesterol (Total-C), HDL-C, TG, fasting blood sugar (FBS), and hemoglobin A1c (HbA1c) levels.

    FINDINGS: Sixty-seven patients entered, and 50 patients (18 male, 32 female) finished the study. Overall, serum HDL-C increased significantly from 39.8 to 45.2 mg/dL in the participants (P = 0.001). HDL-C increased 6.3, 4.4 and 5.0 mg/dL in groups A, B and C, respectively (related significances were 0.017, 0.022 and 0.033, respectively). Significant decrease of serum TG and Total-C occurred in gemfibrozil and combination groups, but not in Vitamin C group. Changes in serum HDL-C between three groups were not significant (P = 0.963). We found a significant decrease in TG and Total-C in the groups B and C (P < 0.05), but no significant changes of TG, Total-C, LDL-C, FBS and HbA1c in group A (P > 0.05).

    CONCLUSION: The results demonstrated that Vitamin C may have beneficial effects on HDL-C in diabetic patients without significant effects on plasma glucose or other lipid parameters; however, its role for the treatment of low HDL-C patients should be evaluated in larger studies.

    Be well!


  4. JP Says:

    Update 07/09/15:

    An example of how not to supplement with vitamins C & E …


    Scand J Med Sci Sports. 2015 Jul 1. doi: 10.1111/sms.12506.

    Vitamin C and E supplementation blunts increases in total lean body mass in elderly men after strength training.

    The aim of this study was to investigate the effects of vitamin C and E supplementation on changes in muscle mass (lean mass and muscle thickness) and strength during 12 weeks of strength training in elderly men. Thirty-four elderly males (60-81 years) were randomized to either an antioxidant group (500 mg of vitamin C and 117.5 mg vitamin E before and after training) or a placebo group following the same strength training program (three sessions per week). Body composition was assessed with dual-energy X-ray absorptiometry and muscle thickness by ultrasound imaging. Muscle strength was measured as one-repetition maximum (1RM). Total lean mass increased by 3.9% (95% confidence intervals: 3.0, 5.2) and 1.4% (0, 5.4) in the placebo and antioxidant groups, respectively, revealing larger gains in the placebo group (P = 0.04). Similarly, the thickness of m. rectus femoris increased more in the placebo group [16.2% (12.8, 24.1)] than in the antioxidant group [10.9% (9.8, 13.5); P = 0.01]. Increases of lean mass in trunk and arms, and muscle thickness of elbow flexors, did not differ significantly between groups. With no group differences, 1RM improved in the range of 15-21% (P < 0.001). In conclusion, high-dosage vitamin C and E supplementation blunted certain muscular adaptations to strength training in elderly men. Be well! JP

  5. JP Says:

    Updated 07/26/15:


    Drug Des Devel Ther. 2015 Jul 1;9:3405-12.

    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.


    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.

    Be well!


  6. JP Says:

    Updated 09/03/15:


    Food Funct., 2015, Advance Article

    Consumption of high-dose vitamin C (1250 mg per day) enhances functional and structural properties of serum lipoprotein to improve anti-oxidant, anti-atherosclerotic, and anti-aging effects via regulation of anti-inflammatory microRNA

    Background: Although the health effects of vitamin C are well known, its physiological effect on serum lipoproteins and microRNA still remain to be investigated, especially daily consumption of a high dosage.

    Objectives: To investigate the physiological effect of vitamin C on serum lipoprotein metabolism in terms of its anti-oxidant and anti-glycation activities, and gene expression via microRNA regulation. Methods We analyzed blood parameters and lipoprotein parameters in young subjects (n = 46, 22 ± 2 years old) including smokers who consumed a high dose of vitamin C (1250 mg) daily for 8 weeks.

    Results: Antioxidant activity of serum was enhanced with the elevation of Vit C content in plasma during 8 weeks consumption. In the LDL fraction, the apo-B48 band disappeared at 8 weeks post-consumption in all subjects. In the HDL fraction, apoA-I expression was enhanced by 20% at 8 weeks, especially in male smokers. In the lipoprotein fraction, all subjects showed significantly reduced contents of advanced glycated end products and reactive oxygen species (ROS). Triglyceride (TG) contents in each LDL and HDL fraction were significantly reduced in all groups following the Vit C consumption, suggesting that the lipoprotein was changed to be more anti-inflammatory and atherogenic properties. Phagocytosis of LDL, which was purified from each individual, into macrophages was significantly reduced at 8-weeks post-consumption of vitamin C. Anti-inflammatory and anti-senescence effects of HDL from all subjects were enhanced after the 8-weeks consumption. The expression level of microRNA 155 in HDL3 was reduced by 49% and 75% in non-smokers and smokers, respectively.

    Conclusion: The daily consumption of a high dose of vitamin C for 8 weeks resulted in enhanced anti-senescence and anti-atherosclerotic effects via an improvement of lipoprotein parameters and microRNA expression through anti-oxidation and anti-glycation, especially in smokers.

    Be well!


  7. JP Says:

    Updated 1/18/16:


    Free Radic Biol Med. 2016 Jan 13.

    Ascorbic acid supplementation improves skeletal muscle oxidative stress and insulin sensitivity in people with type 2 diabetes: Findings of a randomized controlled study.

    AIM/HYPOTHESIS: Skeletal muscle insulin resistance and oxidative stress are characteristic metabolic disturbances in people with type 2 diabetes. Studies in insulin resistant rodents show an improvement in skeletal muscle insulin sensitivity and oxidative stress following antioxidant supplementation. We therefore investigated the potential ameliorative effects of antioxidant ascorbic acid (AA) supplementation on skeletal muscle insulin sensitivity and oxidative stress in people with type 2 diabetes.

    METHODS: Participants with stable glucose control commenced a randomized cross-over study involving four months of AA (2×500mg/day) or placebo supplementation. Insulin sensitivity was assessed using a hyperinsulinaemic, euglycaemic clamp coupled with infusion of 6,6-D2 glucose. Muscle biopsies were measured for AA concentration and oxidative stress markers that included basal measures (2′,7′-dichlorofluorescin [DCFH] oxidation, ratio of reduced-to-oxidized glutathione [GSH/GSSG] and F2-Isoprostanes) and insulin-stimulated measures (DCFH oxidation). Antioxidant concentrations, citrate synthase activity and protein abundances of sodium-dependent vitamin C transporter 2 (SVCT2), total Akt and phosphorylated Akt (ser473) were also measured in muscle samples.

    RESULTS: AA supplementation significantly increased insulin-mediated glucose disposal (delta rate of glucose disappearance; ∆Rd) (p=0.009), peripheral insulin-sensitivity index (p=0.046), skeletal muscle AA concentration (p=0.017) and muscle SVCT2 protein expression (p=0.008); but significantly decreased skeletal muscle DCFH oxidation during hyperinsulinaemia (p=0.007) when compared with placebo. Total superoxide dismutase activity was also lower following AA supplementation when compared with placebo (p=0.006). Basal oxidative stress markers, citrate synthase activity, endogenous glucose production, HbA1C and muscle Akt expression were not significantly altered by AA supplementation.

    CONCLUSIONS/INTERPRETATION: In summary, oral AA supplementation ameliorates skeletal muscle oxidative stress during hyperinsulinaemia and improves insulin-mediated glucose disposal in people with type 2 diabetes. Findings implicate AA supplementation as a potentially inexpensive, convenient, and effective adjunct therapy in the treatment of insulin resistance in people with type 2 diabetes.

    Be well!


  8. JP Says:

    Updated 05/06/16:


    EBioMedicine. 2015 Oct 3;2(11):1735-50.

    Low Red Blood Cell Vitamin C Concentrations Induce Red Blood Cell Fragility: A Link to Diabetes Via Glucose, Glucose Transporters, and Dehydroascorbic Acid.

    Strategies to prevent diabetic microvascular angiopathy focus on the vascular endothelium. Because red blood cells (RBCs) are less deformable in diabetes, we explored an original concept linking decreased RBC deformability to RBC ascorbate and hyperglycemia. We characterized ascorbate concentrations from human and mouse RBCs and plasma, and showed an inverse relationship between RBC ascorbate concentrations and deformability, measured by osmotic fragility. RBCs from ascorbate deficient mice were osmotically sensitive, appeared as spherocytes, and had decreased β-spectrin. These aberrancies reversed with ascorbate repletion in vivo. Under physiologic conditions, only ascorbate’s oxidation product dehydroascorbic acid (DHA), a substrate for facilitated glucose transporters, was transported into mouse and human RBCs, with immediate intracellular reduction to ascorbate. In vitro, glucose inhibited entry of physiologic concentrations of dehydroascorbic acid into mouse and human RBCs. In vivo, plasma glucose concentrations in normal and diabetic mice and humans were inversely related to respective RBC ascorbate concentrations, as was osmotic fragility. Human RBC β-spectrin declined as diabetes worsened. Taken together, hyperglycemia in diabetes produced lower RBC ascorbate with increased RBC rigidity, a candidate to drive microvascular angiopathy. Because glucose transporter expression, DHA transport, and its inhibition by glucose differed for mouse versus human RBCs, human experimentation is indicated.

    Be well!


  9. JP Says:

    Updated 09/16/16:


    Adv Clin Exp Med. 2016 Jul-Aug;25(4):689-700.

    Lower Plasma Levels of Antioxidant Vitamins in Patients with Metabolic Syndrome: A Case Control Study.

    BACKGROUND: Metabolic syndrome (MS) is a coexistence of metabolic risk factors affecting the development of cardiovascular diseases. Reactive oxygen species, which are excessively produced in MS, participate in its pathogenesis. Vitamins A, C and E are an important part of the non-enzymatic antioxidative barrier in humans.

    OBJECTIVES: The aim of the study was to estimate plasma vitamin A, C and E levels and the intake of these vitamins from the diet in patients with MS.

    MATERIAL AND METHODS: The study included 182 patients with MS, 94 men and 88 women, aged 30-65 years (mean 57.31 ± 8.28 years). The control group was comprised of 91 subjects, 56 men and 35 women, aged 41-65 years (mean 57.75 ± 5.84 years). The MS diagnosis was based on IDF criteria. The determination of the serum level of vitamin A, C and E was performed using the spectrophotometric method. The food intake was assessed by 24-h dietary recall.

    RESULTS: The mean plasma vitamin A, C and E levels were significantly lower in MS patients than in the controls (p = 0.05). No correlation was found between vitamin A, C and E intake from the diet and their plasma concentrations in MS patients. Plasma vitamin A, C and E deficiency was observed significantly more often in MS patients than in the control group (15.38% vs. 2.19%, 79.12% vs. 8.79% and 60.45% vs. 5.49%, p < 0.0001, respectively). BMI was the one factor significantly affecting the mean value of vitamin A, C and E levels in MS patients.

    CONCLUSIONS: MS patients demonstrated significantly lower plasma levels of vitamin A, C and E compared to the healthy subjects. Lower plasma levels of antioxidant vitamins with their high intake from the diet indicate antioxidant barrier impairment in MS patients.

    Be well!


  10. JP Says:

    Updated 10/03/16:


    PLoS One. 2016 Sep 29;11(9):e0163571.

    Dietary Vitamin C Intake Reduces the Risk of Type 2 Diabetes in Chinese Adults: HOMA-IR and T-AOC as Potential Mediators.

    Despite growing interest in the protective role that dietary antioxidant vitamins may have in the development of type 2 diabetes (T2D), little epidemiological evidence is available in non-Western populations especially about the possible mediators underlying in this role. The present study aimed to investigate the association of vitamin C and vitamin E intakes with T2D risk in Chinese adults and examine the potential mediators. 178 incident T2D cases among 3483 participants in the Harbin People Health Study (HPHS), and 522 newly diagnosed T2D among 7595 participants in the Harbin Cohort Study on Diet, Nutrition and Chronic Non-communicable Diseases (HDNNCDS) were studied. In the multivariable-adjusted logistics regression model, the relative risks (RRs) were 1.00, 0.75, and 0.76 (Ptrend = 0.003) across tertiles of vitamin C intake in the HDNNCDS, and this association was validated in the HPHS with RRs of 1.00, 0.47, and 0.46 (Ptrend = 0.002). The RRs were 1.00, 0.72, and 0.76 (Ptrend = 0.039) when T2D diagnosed by haemoglobin A1c in the HDNNCDS. The mediation analysis discovered that insulin resistance (indicated by homeostasis model assessment) and oxidative stress (indicated by plasma total antioxidative capacity) partly mediated this association. But no association was evident between vitamin E intake and T2D. In conclusion, our research adds further support to the role of vitamin C intake in reducing the development of T2D in the broader population studied. The results also suggested that this association was partly mediated by inhibiting or ameliorating oxidative stress and insulin resistance.

    Be well!


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