Dr. Julian Whitaker
What benefits come to mind when you think of vitamin C? Colds and flu, most likely—immune support is vitamin C’s main claim to fame. You may have heard of its benefits for the eyes and skin, since this vitamin is one of the key nutrients in many vision supplements and skincare products.
Diabetes, however, rarely comes up. Yet, vitamin C is an essential nutrient for both the prevention and treatment of diabetes and its many complications.
Diabetes Increases Oxidative Stress...
High blood sugar is the defining characteristic of diabetes, but a number of other metabolic abnormalities are also going on, and one of them is oxidative stress.
Hyperglycemia (high blood sugar) increases the production of unstable and highly reactive free radicals. Unless these marauding atoms are neutralized and controlled by antioxidants, which donate electrons to stabilize them, free radicals inflict damage on proteins, fats, DNA, cell membranes, and other cellular structures.
This is the essence of oxidative stress, and it is a major player in insulin resistance and the development and progression of diabetes—as well as a primary cause of nerve and blood vessel damage, cardiovascular disease, kidney failure, vision loss, and other complications of diabetes.
...And Lowers Antioxidant Stores
Because people with diabetes have a higher burden of oxidative stress, they also tend to have lower levels of protective antioxidants. Their antioxidant stores, both endogenous (produced in the body) and exogenous (obtained from food and supplements), get used up defending against excessive free radical activity.
There’s another reason why antioxidant depletion is common in individuals with diabetes. Under normal circumstances, your kidneys reabsorb glucose (sugar) as it filters your blood. When blood sugar levels are high, the kidneys can’t keep up, so excess glucose is flushed out in the urine. That’s why diabetes is associated with excessive urination.
Unfortunately, glucose isn’t the only thing that is excreted. Antioxidants and other essential vitamins and minerals are also lost in the urine. And unless they are replaced, these nutrient losses can adversely affect multiple aspects of health.
Why Vitamin C Matters
Vitamin C is an important antioxidant for people with diabetes for several reasons.
Vitamin C is a primary water-soluble antioxidant, active in tissues throughout the body—plus it regenerates vitamin E, which is the major lipid-soluble antioxidant.
Population studies have linked a high intake of vitamin C with a reduced risk of type 2 diabetes.
Clinical trials show that supplemental vitamin C helps with blood sugar control.
This vitamin must be obtained from food and supplements, as humans are among the few mammal species that cannot produce vitamin C.
We’ve established the heightened risk of oxidative stress in diabetics and the importance of maintaining robust stores of vitamin C and other antioxidants to help keep oxidative damage in check. Now let’s see how that translates into diabetes prevention and treatment.
Vitamin C & Diabetes Prevention
Multiple studies have linked optimal vitamin C status with better insulin sensitivity and lower A1C (a blood test that measures the average blood sugar level over the previous three months). But can taking vitamin C supplements help prevent diabetes?
Although obesity, inactivity, and poor diet are much more heavily weighted risk factors for diabetes, supplemental vitamin C may offer some protection—particularly if your intake of this important antioxidant is low.
In a population study published in Diabetes Care, 232,000 older participants who took vitamin C daily were 9% less likely to develop diabetes, compared to people who didn’t use supplements.
Supplements May Actually Lower Blood Sugar
As for treatment, Australian researchers conducted a small clinical trial involving patients who had been diagnosed with type 2 diabetes for an average of 5.6 years. They were divided into two groups: half who took 500 mg of vitamin C twice a day and the other half who took a placebo. All study participants consumed standardized meals and were followed for four months with continuous glucose monitors.
Vitamin C provided distinct benefits. The average after-meals blood sugar spikes were 36% lower in the vitamin C group than in the placebo group. They also had better overall glucose control—their blood sugar was elevated for nearly three fewer hours a day. In addition, participants in the vitamin C group who had hypertension experienced significant drops in both systolic and diastolic blood pressure.
I’m not suggesting that vitamin C can replace diabetes drugs, berberine, or other proven natural blood sugar-lowering therapies. But as an add-on to diet changes, exercise, weight loss, and other treatments, absolutely!
What About Type 1 Diabetes?
Most of our discussion has been on type 2 diabetes and vitamin C. What about vitamin C and type 1 diabetes?
Type 1 diabetes is also associated with oxidative stress, excessive urination, antioxidant losses, and other harmful metabolic abnormalities. In fact, because type 1 diabetes usually begins earlier in life and blood sugar control is more problematic, risk of complications is even greater. Therefore, boosting antioxidant status is equally—if not more critical—for people with type 1.
How Much Vitamin C Should You Take?
A good diet with plenty of fruits and vegetables is an excellent way to beef up your vitamin C stores. However, I also recommend supplemental vitamin C, 500 mg twice a day—especially if you have diabetes or any other condition that ramps up oxidative stress.