Vitamin C and Diabetes

Author: Dr. Stephen Chaney

Type 2 diabetes is increasing at an alarming rate. Between 1990 and 2010, the number of people in the US living with diabetes has more than tripled. In 2017 the CDC reported that 30.3 million Americans (9.4% of the population) had diabetes. Another 84.1 million had pre-diabetes, a condition which, if left untreated, will develop into diabetes within 5 years.

That is concerning, because type 2 diabetes can have devastating health consequences. It increases inflammation and oxidative damage. It significantly increases your risk of heart disease, Alzheimer’s Disease and some cancers. Then there is kidney disease, nerve pain, and loss of limbs.

It is the hyperglycemia (high blood sugar levels) associated with diabetes that plays a major role in many of these poor health outcomes. That is why so much effort is focused on helping people with type 2 diabetes gain better control of their blood sugar. Management of blood sugar levels in people with diabetes involves both medications and a healthy lifestyle (weight control, a healthy diet, and exercise). Unfortunately, despite their best efforts and the best efforts of their doctors, millions of Americans with diabetes struggle to control their blood sugar levels.

Is there a positive relationship between vitamin C and diabetes?

What if there were a simple, inexpensive intervention that could help diabetics control their blood sugar levels? Recent research suggests that vitamin C might be that intervention. Nobody is claiming that vitamin C is THE solution to blood sugar control. However, the recent research suggests it may be a useful addition to diabetes drugs and a healthy lifestyle.

Does Vitamin C Improve Blood Sugar Control?

The idea that vitamin C may improve blood sugar control has been around for decades based on studies showing that vitamin C helps clear glucose from the circulation. Now, however, we are starting to understand how vitamin C does that.

But before I discuss how vitamin C may improve blood sugar control, the professor in me feels a need to explain what I call Diabetes 101. In type 1 diabetes the pancreas has become unable to produce insulin. In type 2 diabetes tissues have become resistant to the effects of insulin. I will focus on type 2 diabetes.

Glucose is the primary sugar in the bloodstream. Whenever blood sugar (glucose) increases, our pancreas responds by producing insulin. Insulin binds to receptors on our tissues and signals them to take up glucose and rapidly metabolize it. As a result, glucose is rapidly cleared from the circulation and blood sugar levels return to normal.

Type 2 diabetes is caused by insulin resistance. Simply put, our pancreas is still producing insulin, but our tissues have become less efficient at responding to it. Initially, the pancreas responds by overproducing insulin. A new homeostasis is achieved. Blood insulin levels are abnormally high, but glucose is still cleared from the circulation reasonably well. We call this pre-diabetes.

Eventually the pancreas loses the ability to overproduce insulin. Because our tissues are still insulin resistant, glucose is cleared from the circulation slowly. We now have trouble keeping blood sugar levels under control. We call this type 2 diabetes.

There are two major theories at present for why vitamin C may help diabetics control their blood sugar levels:

One theory holds that oxidative stress reduces the ability of the pancreas to release insulin. This theory suggests vitamin C improves insulin release from the pancreas, and the extra insulin overcomes insulin resistance and improves the ability of our tissues to clear glucose from the circulation.
The other theory holds that oxidative stress plays an important role in causing insulin resistance. This theory suggests vitamin C reduces insulin resistance and improves the clearance of glucose from the circulation by this mechanism.

There is some experimental evidence for both mechanisms. It may be that both play a role in vitamin C’s ability to improve blood sugar control.

How Were The Studies Done?

In terms of the effect of vitamin C on blood sugar control, there are two recent studies that have provided intriguing results.

The first study (Y. Song et al, Diabetes Care, 34: 108-114, 2011) was designed to see if supplementation with multivitamins or individual vitamin and mineral supplements affected the risk of developing diabetes among older US adults. It utilized data from the National Institutes of Health – American Association of Retired Persons Diet and Health Study.

The study enrolled 566,402 AARP members ages 50-71 in 1995-1996. Upon entry into the program, participants filled out a dietary survey that included supplement usage. In 2004-2006 a follow-up survey was mailed out to surviving participants that asked about occurrences of major chronic diseases.

Because the onset of a major disease is known to affect supplement usage, all participants with pre-existing diabetes or who developed diabetes prior to 2,000 were excluded from this analysis. Of the remaining 232,007 participants, 217,877 did not have diabetes and 14,130 had developed diabetes between 2000 and the end of the study.

The second study (SA Mason et al, Diabetes, Obesity and Metabolism, 21: 674-682, 2019 ) was a double blind, placebo controlled study design to determine whether supplemental vitamin C improved blood sugar control in people who already had type 2 diabetes.

In this study 31 adults (average age 62 years) were enrolled in the study. All the subjects were borderline obese and had type 2 diabetes. Five of the patients were being managed with lifestyle changes only. The other 26 patients were on one or more diabetes medications to help control their blood sugar levels.

The subjects were advised to avoid supplementation prior to the study. They were then given either 1,000 mg of vitamin C (two 500 mg capsules) or a placebo to take for 4 months. After the first 4-month period they were put on a “washout” protocol with no supplementation. Then they were put on a second 4-month regimen in which they received the opposite tablets (Those who received vitamin C during the first 4 months received a placebo during the second 4 months and vice versa.) Compliance with the protocol was determined by measuring blood levels of vitamin C.

The subjects were outfitted with a continuous blood glucose monitor for a 48-hour period at the beginning and end of each 4-month regimen. They were given standardized meals during those 48-hour test intervals and their blood sugar response to the meals was continuously monitored over the next 48 hours.

The results of the first study were:

Multivitamins and most of the individual supplements tested had no effect on the risk of developing diabetes over the next 10 years. The only supplements that reduced the risk of developing diabetes were vitamin C and calcium.
Vitamin C reduced the risk of developing diabetes by 9%.
The benefits of vitamin C appeared to be limited to individuals who did not use multivitamins and who had low dietary intake of vitamin C (No surprises there. Supplementation is usually most effective when it is filling in nutritional gaps).

This study has several obvious limitations:

It is an association study, so it does not prove cause and effect.
It does not tell us whether vitamin C prevents diabetes or simply improves blood sugar control in people who are borderline diabetic.
It did not measure how much supplemental vitamin C people were taking. However, based on what is available in the marketplace, it is probably safe to assume it was between 500 and 1,000 mg/day.

However, this study did lay the groundwork for the second study.

The results of the second study were that 4 months of vitamin C supplementation reduced:

The blood sugar response to standardized meals by 36%.
The duration of high blood sugar following a standardized meal by 1.7 hours.
The amount of time during the day with high blood sugar levels by 2.8 hours.

These are all important improvements for anyone with type 2 diabetes. In the words of the authors: “The improvement in total daily time spent with hyperglycemia [high blood sugar] is of potential clinical importance as the risk of complications in type 2 diabetes is strongly associated with previous hyperglycemia.”

The authors went on to say: “Compliance in the present study was high [people did not find it difficult to take 2 tablets a day] and the number of reported adverse effects was low, suggesting that vitamin C may be safely and consistently used in addition to [emphasis mine] primary diabetes treatment. Given the potential side effects with common anti-diabetic medications…, the idea that a relatively benign and inexpensive vitamin supplement might play a role in managing diabetes has particular appeal.”

Note: This was a very well-designed study. Its weakness is its small size. While it is consistent with other recent studies, larger clinical trials are needed to confirm this effect.

What Do These Studies Mean For You?

The idea that vitamin C may help with blood sugar control has been around for decades. These studies provide experimental support for that idea. While both studies have limitations, they are consistent with other recent studies. Much more research is needed, but it is good to finally see the hypothesis being rigorously tested.

So, what do these studies mean for you? Here is the take home message:

Although more studies are needed, vitamin C appears to help with blood sugar control.
We don’t know how much vitamin C is needed, but the most recent study was done with 1,000 mg/day. That is more than can be obtained from diet alone.
The improvement in blood sugar control was significant, but it was not huge. Vitamin C will not replace a healthier weight, a healthy lifestyle, and exercise.
You should think of vitamin C as something you add to the treatment plan your doctor recommends for type 2 diabetes. At best it may allow your doctor to reduce the amount of medication they prescribe.

If you have type diabetes, here are my recommendations:

If you are overweight, try to attain and maintain a healthier weight.
Eat a whole food, primarily plant-based diet. Avoid sodas, sweets, and highly processed foods. Eat a variety of fruits, vegetables, whole grains, and beans in their natural, unprocessed state. Include small amounts of meat, eggs, and dairy. Think of them as the garnish, not the main course.
Add a daily vitamin C supplement.
If that is not enough, ask your doctor what medications he or she recommends.

Other nutrients that may help are chromium, taurine and alpha lipoic acid. Herbs that may help are bitter melon and gymnema.

The Bottom Line

What is the association between vitamin C and diabetes? The idea that vitamin C may help with blood sugar control has been around for decades. Two recent studies provide experimental support for this idea. The second study showed that 4 months of 1,000 mg/day vitamin C supplementation reduced:

The blood sugar response to standardized meals by 36%.
The duration of high blood sugar following a standardized meal by 1.7 hours.
The duration of the day with high blood sugar levels by 2.8 hours.

While this study has limitations, it is consistent with other recent studies. Much more research is needed, but it is good to finally see the hypothesis that vitamin C improves blood sugar control being rigorously tested.

So, what do these studies mean for you? Here is the take home message:

Although more studies are needed, vitamin C appears to help with blood sugar control.
We don’t know how much vitamin C is needed, but the most recent study was done with 1,000 mg/day. That is more than can be obtained from diet alone.
The improvement in blood sugar control was significant, but it was not huge. Vitamin C will not replace a healthier weight, a healthy lifestyle, and exercise.
You should think of vitamin C as something you add to the treatment plan your doctor recommends for type 2 diabetes. At best it may allow your doctor to reduce the amount of medication they prescribe.

For more details and my recommendations read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.