High Doses of Vitamin C Supplement Increase Blood Glucose Levels

Cause False Diabetes Diagnosis

Donald R. Branch, PhD

| Sep 1, 1999

According to the July issue of Diabetes Care, high doses of supplementary vitamin C may cause an unexpected elevation of blood sugar levels and false diagnosis of type 2 diabetes.

Donald R. Branch, PhD, reports the case of a 49-year-old, slightly obese man who took high levels of vitamin C, causing high fasting (121 mg/dl) and after-meal (220 mg/dl) blood sugar levels. The man, who had earlier been diagnosed as a potential candidate for type 2 diabetes based on his age, obesity and repeat elevated blood sugar readings, had taken 4,500 mg. per day of a synthetic, unsweetened vitamin C product for the past five years.

The patient was asked to discontinue the supplement and, after seven days, morning blood sugar averages dropped to 99 mg/dl. He then restarted vitamin C supplements in dosages of 4,500 mg. per day, and morning blood sugars rose to 110 mg/dl. He discontinued the supplement again and, after one week, blood sugars dropped to 79 mg/dl.

Branch says that elevated blood sugars, as a result of taking such a high dose of vitamin C, "...could result in a misdiagnosis of diabetes and/or additional, unnecessary testing, as in this case." He adds that "..vitamin C-induced production of glucose may interfere in the glucose monitoring of true diabetic patients."

Branch says that the man reduced his vitamin C intake to 1,500 mg. per day, and his blood sugars returned to the normal range. He says that vitamin C, taken in dosages of 1,500 to 2,000 mg. per day, has been proven to effectively reduce blood sugar and HbA1c levels. Also, research suggests it prevents kidney injury in diabetic rats.

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Categories: A1c Test, Blood Glucose, Blood Sugar, Diabetes, Supplements, Type 2 Issues, Vitamins

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Posted by Anonymous on 14 May 2008

This may be my problem. I have been taking megadoses of Vitamin C and my doctor says I'm pre-diabetic.

Posted by Anonymous on 1 July 2008

Its interesting that this study does not mention if this person ate sweats, fruits, white bread, or white pasta products at the time.

Posted by Anonymous on 30 November 2010

I had no idea Vitamin C caused elevated glucose readings. Husbands drs. have told him to increase his Vit C intake, to ward off colds and build up his immume system. But with diabetes, that's like beating a dead horse even more....dead.

Posted by Anonymous on 19 April 2011

when using 1000 mg vit c , my bloog sugar became elevated, when I stopped taking the suppliment I was using , my blood sugar went back to normal, I am 68 years old.

Posted by Anonymous on 21 May 2013

There is a misunderstanding here:

Vitamin C has a molecular structure very similar to glucose and the test for serum glucose picks up both molecules making the measurement inaccurate. Vitamin C does not boost blood glucose, in fact according to recent research if actually does the opposite, one example: http://www.ncbi.nlm.nih.gov/pubmed/18160753.

" daily consumption of 1000 mg supplementary vitamin C may be beneficial in decreasing blood glucose and lipids in patients with type 2 diabetes and thus reducing the risk of complications "

Posted by Anonymous on 19 November 2014

My current and former doctors have warned me that I'm nearly diabetic at 62 years old. No family history of it.
I take 560mg of vitamin C daily which has served me well. I've had 2 colds in the past 7 years. My A1c goes up
and down. Cutting back on sweets and quitting regular cola drinks has dropped it from 6.7 to 5.5. I barely watch
my carbs at all. I'll have to skip my multivitamin and half packet of Emergen-C for my next test.

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