Vitamin C And Diabetes

People with diabetes are more prone to have low levels of vitamin C. A higher need for vitamin C arises because of diabetes linked complications. A low level of vitamin C has a tendency to promote high HbA1c levels.


The Function of Vitamin C

Vitamin C is a water-soluble vitamin and is also known by the name Ascorbic acid.

Vitamin C is an essential cofactor in a number of enzyme reactions in our body, including:

  • In the synthesis of collagen, carnitine, and catecholamines
  • Is a powerful antioxidant
  • Promotes a stronger immune system
  • Helps regenerate other antioxidants like vitamin E
  • Involved in metabolism of cholesterol & bile acids
  • Involved in iron absorption

Vitamin C is not made in our body, which means that it has to be taken by diet.

Vitamin C: Daily Requirements for Type 2 Diabetes

The recommended daily allowance (RDA) for normal people is 75 mg for women and 90 mg for men, with an upper limit of 2000 mg daily.

However, for people with type 2 diabetes and prediabetes, you may need more.

According to research, diabetics have approximately 30% less vitamin C circulating in their blood compared to non diabetics.   

As the vitamin C level declines, the HbA1C level increases.  

So why are your vitamin C needs higher when you have diabetes?  

A high oxidative stress caused by increased free radical production is common in type 2 diabetes. When our body is in chronic oxidative stress, there is a continuous fight between pro-oxidants and antioxidants.  

When this fight turns worse, the level of antioxidant resources gets depleted, leading to a decline in antioxidant levels (remember, vitamin C is one of our body’s central antioxidants).

Moreover, when blood sugar levels are elevated, vitamin C can’t be absorbed well into the cells and you can have increased urine losses.

Therefore, for a person with type 2 diabetes, the requirements for vitamin C are closer to 95 mg/day for women and 120 mg/day for men (~30% higher than the RDA), especially if you have poorly controlled diabetes.  

Vitamin C and Blood Sugar Levels

There is some evidence that shows taking vitamin C supplements may assist with better glucose control.  

large review concluded that vitamin C supplementation lowered fasting glucose levels by 20 mg/dL (1.11 mmol/L) and reduced HbA1c by 0.46%.

Another review showed vitamin C supplementation reduced random glucose levels by 8 mg/dl (0.44 mmol/L) and fasting levels by 24 mg/dL (1.36 mmol/L).

While these studies do indicate that vitamin C supplementation may improve blood glucose levels, however, all the trials provide participants with different amounts of vitamin C, ranging from 100 to 1000 mg/day.

Therefore, it is difficult to say how much Vitamin C is required to lower glucose and how long you need to take it.

Vitamin C as an Antioxidant

Vitamin C is a potent antioxidant. The role of antioxidants in our body is to neutralize and control the free radicals which cause damage (oxidative stress) and increase the likelihood of diabetes linked complications and all other inflammation related diseases.

Antioxidants can help prevent and repair free radical damage caused by oxidative stress, which in turn helps to improve insulin secretion and glycemic control.

Antioxidants found in whole fruits and vegetables, including vitamin C, can help prevent diabetes linked complications.

However, more research is needed on this, most likely because vitamin C works as a part of an elaborate network of antioxidants which work synergistically to exert their benefits.

Vitamin C Supplementation Dosage & Side Effects

Vitamin C supplements are available in various forms – ascorbic acid, sodium ascorbate, calcium ascorbate and a combination of any of these forms.

Ascorbic acid is the ideal form of vitamin C, as it is inexpensive and has the same absorption tendency as the naturally occurring vitamin C in foods.  

Vitamin C supplements are equally good in tablet, powder and liquid form.

Are vitamin C supplements safe?  

Overall vitamin C supplements are considered pretty safe.

Taking 30 to 100 mg/ day supplemented vitamin C results in a steady increase in blood levels of vitamin C. At 200 mg/ day, complete absorption is generally achieved. Once saturation of tissues is achieved, the excess vitamin C is excreted in urine.

Interestingly, research indicates that vitamin C supplements (400 mg/day or more) reduce risk of fatal and nonfatal coronary heart disease in people with diabetes. However, other research suggests that levels equivalent to, or over 300 mg/d are associated with the potential for an increased risk of cardiovascular disease in individuals with type 2 diabetes.  

Considering the above research studies, it’s good to stick to around 200 mg/ day is better.

One side effect of rapid vitamin C supplementation can be diarrhea. However, it’s often temporary but it’s good to be aware initially.

Like they say, “Natural is always the best”, consuming a diet including plenty of vitamin C-rich foods provides significantly more benefit than supplementation alone. And consuming foods is more safe.

Sources of Vitamin C

Vitamin C is naturally found in many fresh vegetables and fruits – foods that are ideal as part of the typical diabetes diet.

Rich sources of vitamin C include (for 1 cup):


  • Yellow bell peppers – 341 mg
  • Red bell peppers – 203.8 mg
  • Green bell peppers – 217.6 mg
  • Mustard spinach – 195 mg
  • Broccoli – 106 mg
  • Brussel sprouts – 100 mg
  • Kale – 87 mg

Low Carb Fruits (1/2 cup):

  • Lemon – 112 mg
  • Strawberries – 89 mg
  • Grapefruit – 85 mg

Since the vitamin C content of food is reduced by prolonged shelf life and cooking, raw vegetables and fruits provide the highest vitamin C.

Incorporating Vitamin C into Your Daily Diet

By trying to eat one serving of fruit and at least four servings of vegetables daily, one can easily consume more than 200 mg of vitamin C.  

Ensure to focus on raw foods instead of cooked foods, due to losses of vitamin C in the heating process. Also, opt for fresh foods.

However, if you prefer cooked vegetables, steaming preserves more vitamin C in comparison to boiling or roasting.


As per current research, Vitamin C can help reduce oxidative damage and improve blood sugar and A1c levels. However, more research data is needed on this. Your need for vitamin C with type 2 diabetes and prediabetes increases so ensure to get adequate intake every day by eating lots of fresh fruits and vegetables.

FAQs(Frequently asked Questions)

Can diabetics eat bananas?

Diabetics can eat green bananas because they are low in sugar in comparison to ripe bananas.

What is the best natural food to lower blood sugar in Ayurveda?

The best is bitter melon to lower blood sugar. Diabetics should consume bitter melon juice daily in small amounts.

How much bitter melon juice or karela juice daily to lower blood sugar?

Ideally, it should be 30-50 ml once or twice a day.

What precautions you need to take while taking bitter melon juice or karela juice for diabetes?

Do not overdo the recommended amount of 30-50 ml once or twice a day as excessive amounts can cause stomach irritation.

My name is Amanpreet Kaur Samra. M.S. Biochemistry. I'm the founder and writer of this blog. I have been teaching Biochemistry for a good number of years. I started this blog because I have always been very passionate about writing, in particular about Nutrition and Healthy Weight Loss.

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