Vitamin C Diabetes: Benefits for Blood Sugar & Complications

People with diabetes are more likely to have low levels of vitamin C. Having diabetic complications can also increase your need for vitamin C. And interestingly, if you have lower levels of vitamin C, this may promote higher HbA1c levels.

Keep reading to discover more about the role of vitamin C in the body, supplements, foods and how vitamin C can be of benefit in your diabetes management routine.

The Role of Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin.

Vitamin C is an essential cofactor in many enzyme reactions in the body, including:

• Aiding with the synthesis of collagen, carnitine, and catecholamines
• Being a powerful antioxidant
• Promotes a healthier immune system
• Helps regenerate other antioxidants such as vitamin E
• Involved in metabolism of cholesterol and bile acids
• Helps enhance the bioavailability of iron from foods

Vitamin C is not made in the human body, which means you need to consume it through food or supplements.

Being that vitamin C is the dominant antioxidant found in the blood and tissues throughout the body, it’s no surprise that it’s best known for its powerful antioxidant capabilities.

Vitamin C: Daily Requirements for Type 2 Diabetes

The recommended daily intake (RDI) for the general adult population 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, people with diabetes have approximately 30% less vitamin C circulating in their blood compared to the general population.

If you have type 2 diabetes along with complications, you may even have lower levels compared to those without diabetes related complications. And that’s not great because large studies have found that vitamin C levels and HbA1c levels are associated.

In fact, as your vitamin C level declines researchers have found that HbA1c level increases.

Why are your vitamin C needs higher when you have diabetes?

Oxidative stress caused by increased free radical production is common in type 2 diabetes. When your body is in a chronic state of oxidative stress, there is an unseen battle going on between pro-oxidants and antioxidants.

As the battle rages on in your body, your level of antioxidant resources get depleted, leading to a decline in your antioxidant levels (remember, vitamin C is one of the body’s central antioxidants).

On top of this, when your blood glucose levels are elevated, vitamin C can’t be absorbed into cells as efficiently and you can have increased urine losses.

Therefore, as a person with type 2 diabetes, your requirements for vitamin C may be closer to 95 mg for women and 120 mg/day for men (~30% higher than the RDI), 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.

For instance, a large review concluded that vitamin C supplementation lowered fasting glucose levels by 1.11 mmol/L and reduced HbA1c by 0.46%.

Another review showed vitamin C supplementation reduced random glucose levels by 0.44 mmol/L and fasting level by 1.36 mmol/L.

A study from Deakin University found that taking 500mg twice a day helped to lower blood sugar levels and prevent blood sugar spikes after a meal by up to 36%.

Vitamin C as an Antioxidant

Vitamin C is a powerful antioxidant. The role of antioxidants in the body is to neutralise and control free radicals – cells that cause damage (oxidative stress) and increase the likelihood of diabetic complications.

Antioxidants can help prevent and repair free radical damage caused by oxidative stress, which in turn improves insulin secretion and glycaemic control.

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

However, there is little evidence to support that antioxidant supplements have the same effect. Most likely because vitamin C works as part of an intricate network of antioxidants all working together to exert their benefits.

Vitamin C to Reduce Diabetes Complications

Another review from Deakin University suggests that boosting vitamin C levels, especially in those who are deficient, can help reduce risk for diabetes complications like heart disease, high blood pressure, and foot ulcers.

This may be due to vitamin C’s antioxidant influence, as outlined above.

Vitamin C Supplements for Type 2 Diabetes

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

Ascorbic acid is the preferred form of vitamin C, as it is affordable and has the same absorption capability as the naturally-occurring vitamin C in foods.

You can purchase vitamin C supplements in tablet, powder and liquid form.

We prefer a powdered vitamin C with bioflavonoids, as this helps with increased absorption and bioavailability of the vitamin C.

Are vitamin C supplements safe?

Overall, vitamin C supplements are considered safe.

Consuming 30 to 1000 mg/ day of supplemented vitamin C results in a steady increase in blood levels of vitamin C. At 2000 mg/ day, complete absorption is generally achieved. Once saturation of tissues is reached, any vitamin C your body doesn’t utilise is excreted in urine.

In general, modest doses of 500-1000mg per day are considered safe; and keeping to a maximum of 2000 mg/ day is probably the best practice.

**Always consult with your doctor prior to starting any supplementation, especially if taking medications or when considering higher dosages.

One side effect of increasing vitamin C rapidly can be diarrhoea. It’s often temporary but something to be aware of initially.

Another point that has been mentioned above, and something researchers agree upon, is that in most cases, consuming a diet that includes plenty of vitamin C-rich food provides significantly more benefit than supplementation alone. And consuming foods is obviously safe.

So the message here is: eat plenty of fresh produce to get your daily dose of vitamin C, even if you do intend on supplementing.

Sources of Vitamin C

Vitamin C is naturally found in many fresh vegetables and fruits – foods that are great as part of your diabetic diet!

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

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

Incorporating Vitamin C into Your Daily Plan

By focusing on eating one serving of fruit and at least four servings of veggies daily, you can easily consume more than 200 mg of vitamin C.

Remember to focus on raw foods instead of cooked foods, due to the losses of vitamin C in the heating process.

However, if you prefer cooked vegetables, steaming preserves more vitamin C compared with boiling or roasting.

A large salad that includes the foods and amounts listed below provides 200 mg of vitamin C and only 12 grams of carbohydrates:

• 2 cups spinach (300 mg vitamin C, 1g carb)
• Half cup red capsicum (100 mg vitamin C, 3g carb)
• 1 medium tomato (20 mg vitamin C, 3g carb)
• Half cup of strawberries (50 mg vitamin C, 5g carb)

Another suggestion would be raw broccoli, cauliflower and green capsicums with hummus or cottage cheese.

Eating one cup of a combination of these raw veggies provides approximately 70 mg of vitamin C and only 4 grams of carbs. This is more than half your daily requirement in a quick and easy snack option!

Conclusion: Vitamin C and Diabetes

Vitamin C can help reduce oxidative damage, improve blood sugar and HbA1c levels, reduce risk of diabetes complications, along with helping to boost your overall health.

Your need for vitamin C with type 2 diabetes and prediabetes can increase, so ensure you get adequate intake each day by eating lots of fresh produce, or by adding an additional supplement.