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.