Vitamin C and type 2 diabetes

“Vitamin C can help to lower the blood sugar of diabetic patients as well as lowering their blood pressure. A breakthrough finding!” This was widely reported in the major television news in Australia recently. A friend is excited about the news as he has both diabetes and hypertension. He wants me to comment on the findings.

Good news indeed, given that diabetes is now a major public health issue worldwide with almost 1 in 10 adults in the world has diabetes [1]. The number is even more staggering for developed countries. If vitamin C can be used to treat diabetes, given its wide availability and low cost, it can benefit a lot of patients. However, before we get too carried away with this possibility, let’s look at what is the research behind it.

The research article published in Diabetes, Obesity and Metabolism

The recent news reports were sparked by a study done by scientists from Deakin University in Australia. The findings of the study have just been published in an international journal, namely “Diabetes, Obesity and Metabolism”. This study involved 31 participants with type 2 diabetes [2]. The participants were given either 500mg of vitamin C (L-ascorbic acid) or placebo to take twice a day for 4 months. The study found taking vitamin C helped to reduce the spike of blood sugar after a meal by 36%. The participants also have lower blood sugar levels (average -1.1 mmol/L) and lower blood pressure (systolic: −7 mm Hg, and diastolic: −5 mm Hg) after vitamin C supplementation [2].

Diabetes is a pandemic affecting close to 10% of the world adult population.

Overall this is a well-designed study. For example, to ensure consistent measurement of the blood sugar level, the participants had to attend the research clinic for two consecutive days at the start and end of the 4-month period. Blood sugar level was measured by having each participant wearing a device which continuously monitors blood sugar for 48 hours. The participants were also given standardized meals to eat during this period to ensure consistency in the results. Hence, the findings represent strong evidence to support the use of vitamin C for blood sugar management in type 2 diabetic patients [2].

Vitamin C supplementation was also found to lower blood pressure in patients with type 2 diabetes

Nevertheless, this does not mean that vitamin C can replace any diabetes medication. In this study, vitamin C was not used as the main treatment for diabetes. The participants continue to take their medications for type 2 diabetes throughout the study. Hence, it will be wrong to jump the gun and claim that vitamin C is a cure for type 2 diabetes!

A systematic review published in 2017

The research on the effects of vitamin C on blood sugar control is not new. An earlier article published in the European Journal of Clinical Nutrition already found 22 studies on the topic [3]. By analysing the results of these studies, the authors concluded that, in general, vitamin C did not change blood sugar level, HbA1c (a blood test that helps to diagnose and monitor people with diabetes) and insulin concentrations. Only in patients with type 2 diabetes that took vitamin C for more than 30 days that vitamin C was found to reduce blood sugar level by −0.44 mmol/l on average. Older people seem to respond better to vitamin C supplementation in term of insulin response [3]. Therefore, this study also supports vitamin C supplementation in patients with type 2 diabetes.

Antioxidants Free radicals Lobo et al.,
Vitamin C is a potent antioxidant that protect cells from free radicals. Here is a illustration of how it works.

KScientists are still not sure exactly how vitamin C works to reduce blood sugar level in the body. We know that increased production of free radicals can affect how insulin works in the body and the absorption of glucose into cells as experienced by patients with type 2 diabetes. With vitamin C being a potent antioxidant that protects the tissues from harmful free radicals, it makes sense that increased intake of vitamin C can help to reduce the free radicals that affect the regulation of blood sugar levels. Most people with diabetes also have lower vitamin C level in their blood compared others who have no diabetes, as observed in another study [4]. Hence, taking the vitamin C supplement can supply the needed antioxidants to fight the free radicals, which indirectly improve blood sugar control.

Diabetes: take 1000mg vitamin C daily to better manage blood sugar.

With such supporting evidence, if you have type 2 diabetes, it is definitely a good idea to take 1000mg of vitamin C daily. It can help you to control your blood sugar better. Start today if you have not already done so!  


[1]        “Diabetes in Singapore.” [Online]. Available: [Accessed: 22-Feb-2019].

[2]        S. A. Mason, B. Rasmussen, L. J. C. van Loon, J. Salmon, and G. D. Wadley, “Ascorbic acid supplementation improves postprandial glycaemic control and blood pressure in individuals with type 2 diabetes: Findings of a randomized cross-over trial,” Diabetes, Obes. Metab., vol. 21, no. 3, pp. 674–682, Mar. 2019.

[3]        A. W. Ashor, A. D. Werner, J. Lara, et al., “Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials,” Eur. J. Clin. Nutr., vol. 71, p. 1371, Mar. 2017.

[4]        R. Wilson, J. Willis, R. Gearry, et al., “Inadequate Vitamin C Status in Prediabetes and Type 2 Diabetes Mellitus: Associations with Glycaemic Control, Obesity, and Smoking,” Nutrients, vol. 9, no. 9, p. 997, Sep. 2017.

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