Is Vitamin C Useful for Type-2 Diabetes?

Check out this answer from Consensus:

Vitamin C supplementation shows promise in improving glycemic control and lipid profiles in individuals with T2DM. However, due to the limitations of the current evidence, vitamin C cannot yet be recommended as a standard therapy for T2DM. Further research is needed to confirm these findings and determine the most effective supplementation strategies.

Type-2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and hyperglycemia. Managing T2DM often involves lifestyle modifications and pharmacological interventions. Recently, there has been growing interest in the potential role of vitamin C supplementation in improving glycemic control and reducing cardiovascular risk factors in individuals with T2DM. This article reviews the current evidence on the efficacy of vitamin C in managing T2DM.

Glycemic Control

Several studies have investigated the impact of vitamin C on glycemic control in T2DM patients. A systematic review and meta-analysis of randomized controlled trials (RCTs) found that vitamin C supplementation significantly reduced HbA1c levels and fasting blood sugar (FBS) in T2DM patients, although the evidence quality was low to moderate1. Another study demonstrated that high-dose vitamin C supplementation (1000 mg/day) significantly decreased FBS, HbA1c, and serum insulin levels, suggesting improved glycemic control5. Additionally, a double-blind study showed that vitamin C combined with metformin significantly improved FBS, postmeal blood glucose (PMBG), and HbA1c levels compared to metformin alone8.

Lipid Profile

Vitamin C’s effect on lipid profiles in T2DM patients has also been explored. A meta-analysis indicated that vitamin C supplementation significantly decreased triglycerides (TG) and total cholesterol (TC) levels but had no significant effect on low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels3. Another systematic review supported these findings, showing that vitamin C intake improved lipid profiles by reducing TG and TC levels, although it did not significantly affect LDL and HDL9. However, some studies reported no significant changes in lipid profiles with vitamin C supplementation10.

Cardiovascular Risk Factors

Cardiovascular disease (CVD) is a major complication of T2DM, and managing cardiovascular risk factors is crucial. Vitamin C has been shown to reduce systolic and diastolic blood pressure in T2DM patients, although the evidence quality was low1. Additionally, vitamin C intake was associated with improved endothelial function and reduced markers of inflammation and oxidative stress, which are important for cardiovascular health9. However, some studies found no significant effect of vitamin C on blood pressure, oxidative stress, or endothelial function7.

Limitations and Future Research

While the current evidence suggests potential benefits of vitamin C supplementation in improving glycemic control and lipid profiles in T2DM patients, the findings are not conclusive. Many studies were short-term and involved small sample sizes, limiting the generalizability of the results. Long-term, high-quality RCTs with larger sample sizes are needed to confirm these findings and establish optimal dosing and duration of vitamin C supplementation.

Is vitamin C useful for type-2 diabetes?

Cornelie Nienaber-Rousseau has answered Likely

An expert from North-West University in Nutrition

According to Bajaj and Khan (2012) hyperglycemia promotes auto-oxidation of glucose to form free radicals and antioxidans such as vitamin C (ascorbic acid) could reduce the complications of these free radicals. Also see Balbi et al. (2018).

A systematic review and meta-analysis summarising 22 randomised controlled trials indicated that vitamin C did not modify fasing glucose, HbA1c (long term marker for glycemic control) or insulin concentrations (Ashor et al., 2017). However a subgroup analysis indicated that vitamin C reduced glucose concentration in type 2 diabetic patients in interventions with durations greater than 30 days. Recently, findings from a randomized cross-over trial involving a small sample of 31 type 2 diabetic patients by Mason et al. (2019) indicated improved postprandial and 24-hour glycemia and decreased blood pressure after 4 months of supplementation with vitamin C vs a placebo. However, this research will need to be replicated in larger groups with durations longer than 30 days or 4 months long to confirm the finding of Mason et al. (2019) and to make evidence based recommendations on vitamin C intake and type 2 diabetes.

Is vitamin C useful for type-2 diabetes?

Walter Hsu has answered Uncertain

An expert from Iowa State University in Biochemistry, Pharmacology

Vitamin C is an antioxidant and we know that oxidative stress may be involved in insulin resistance, which is associated with type 2 diabetes (Hurrle S & Hsu WH: The etiology of oxidative stress in insulin resistance. Biomedical Journal, 40:257-262, 2017). Therefore, vitamin C administration on the long-term basis might benefit patients with type 2 diabetes. 

A recent meta-analysis concluded : a “greater reduction in glucose concentrations observed in patients with (type 2) diabetes, older individuals and with more prolonged supplementation. Personalized interventions with vitamin C may represent a feasible future strategy to enhance benefits and efficacy of interventions.”

Is vitamin C useful for type-2 diabetes?

Glenn D Wadley has answered Likely

An expert from Deakin University in Physiology, Diabetes

For some glucose measures vitamin C it rates as “likely”, and others it rates as “uncertain”. Given more of the measures are in the “likely” column, I’ve gone with this rating, but more research is needed. Importantly, please discuss any potential changes to your diabetes treatment plan with your doctor first.

 In short, there is now evidence from well-designed but small (30-50 people with T2D) studies to demonstrate 1g/ day vitamin C lowers several blood glucose measures, such as fasting glucose, 24hr blood glucose levels and the post-meal blood glucose spike. However, most studies that have reported no effect of vitamin C have used doses much lower than 1 g/day. There is little evidence >1g/day provides additional benefit.

 In support of a role for vitamin C supplementation in the treatment of T2D, a recent systematic review and meta-analysis (which collates and analyses all published studies)(1) found that vitamin C supplementation of up to four months duration significantly lowers blood glucose levels by ~0.44 mmol/l (8 mg/dl) in people with T2D. We recently found it lowered blood glucose levels across the day by ~0.8 mmol/l (14 mg/dl) (2). Similar evidence also supports vitamin C having a moderate effect on lowering blood pressure.  

However, it is still uncertain if vitamin C lowers HbA1c levels, which is a measure of long-term blood glucose control that most clinicians focus on. There are several reasons why the effect on this measure rates as “uncertain” rather than “unlikely”. First, since HbA1c is a long-term measure of control, most of the available studies aren’t designed adequately to find an effect. This is because they aren’t long enough or don’t allow a long enough washout period between vitamin C and placebo treatments (in the case of cross-over studies). Another key factor is the starting level of HbA1c. For the studies that we have conducted, we recruit people via public advertisements – and the result is usually a cohort that is interested in their health and already compliant with their T2D medications and typically have HbA1c levels towards the lower end and thus with less room to improve. To answer the question properly we need to conduct a large study in people with T2D over a much longer period and in a group that has a broader range of HbA1c levels. 

References

1. Ashor, Werner, Lara, Willis, Mathers and Siervo, Eur J Clin Nutr, 2017, 71(12): 1371-1380.
2. Mason, Rasmussen, van Loon, Salmon and Wadley, Diabetes Obes Metab, 2019, 21(3): 674-682.

Is vitamin C useful for type-2 diabetes?

Hayder Al-Aubaidy has answered Likely

An expert from La Trobe University in Biochemistry

Vit C proved to be a natural antioxidant, so it can help improve the glycemic control via reducing the overall oxidative stress, however, studies are needed to clarify the underlying mechanisms for this complex effect.

Is vitamin C useful for type-2 diabetes?

Anitra Carr has answered Likely

An expert from University of Otago in Vitamin C

Yes – vitamin C is useful for type-2 diabetes. People with type-2 diabetes have a lower vitamin C status compared with healthy people [1]. Because type-2 diabetes is associated with enhanced inflammation and oxidative stress, additional vitamin C intake may help decrease these conditions due to its antioxidant and anti-inflammatory functions. Meta-analysis (comparison of multiple studies) has also indicated that supplementation with vitamin C may help with glycaemic control in people with type-2 diabetes [2,3].

References:

1.       Wilson R, Willis J, Gearry R, Skidmore P, Fleming E, Frampton C, Carr A. Inadequate vitamin C status in prediabetes and type 2 diabetes mellitus: Associations with glycaemic control, obesity, and smoking. Nutrients. 2017;9(9):E997.
2.         Tabatabaei-Malazy O, Nikfar S, Larijani B, Abdollahi M. Influence of ascorbic acid supplementation on type 2 diabetes mellitus in observational and randomized controlled trials; a systematic review with meta-analysis. J Pharm Pharm Sci. 2014;17(4):554-82.
3.         Ashor AW, Werner AD, Lara J, Willis ND, Mathers JC, Siervo M. Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials. Eur J Clin Nutr. 2017.