Vitamin C has shown some fairly impressive cholesterol lowering abilities in previous studies, however the importance of vitamin C in both preventing and treating diabetes has only recently come to light. The only published study on the issue of vitamin C and diabetes risk was published in 2008 and found huge reductions in diabetes risk for those with high levels of vitamin C.
The study, which was published in the journal Archives of Internal Medicine, was conducted by British researchers based at the University of Cambridge. This was a large prospective study that involved more than 21,000 men and women from the European Prospective Investigation of Cancer–Norfolk study. The participants, who were initially free of diabetes, had their blood vitamin C levels measured at a beginning of the study and were then followed over a 12 year period.
Over the course of the study, 735 new cases of diabetes were diagnosed. The researchers found that in the unadjusted model, men and women in the top 20% for vitamin C levels were a massive 77% less likely to develop diabetes than those in the bottom 20% for vitamin C levels. Vitamin C levels in the top 20% represented levels above 1.1 mg/dL and 1.29 mg/dL in men and women respectively while the bottom 20% had levels below 0.56 mg/dL and 0.77 mg/dL.
After adjusting the results for several confounders including age, sex, family history of diabetes, alcohol and smoking levels, physical activity, and BMI, the link between diabetes and vitamin C was reduced, but those in the top 20% for vitamin C still showed an impressive 62% reduction in risk.
The odds ratios for the unadjusted and fully adjusted models are shown on the graph to the right.
The researchers also looked at the effect of fruit and vegetable intake on the risk of diabetes, however vitamin C levels were found to be a better predictor of diabetes risk than fruit and vegetable consumption. Those in the top 20% for fruit and vegetable intake were 23% and 32% less likely to develop diabetes in the unadjusted and adjusted models respectively compared to those in the bottom 20%.
Vitamin C has also demonstrated the ability to improve glucose metabolism in both diabetic and non-diabetic subjects. A study, published in the journal Endocrinology and Metabolism in 1994, looked at the effects of vitamin C infusion on 10 healthy and 10 diabetic individuals. Although Vitamin C did not improve insulin response to glucose, it did improve glucose disposal in both groups of subjects through improvements in non-oxidative glucose metabolism. Glucose metabolism refers to the mechanism by which glucose is converted into glycogen by the liver for longer term energy storage. Impaired glucose metabolism is often found in type-2 diabetics.
Most studies find that diabetics have lower average levels of vitamin C in their blood compared to non-diabetics. A study published in the journal Diabetic Medicine in 2009 found significantly lower levels of vitamin C in the blood of diabetics vs non-diabetics despite similar intakes of vitamin C. This suggests that vitamin C requirements may be higher in diabetics than non-diabetics. There is good evidence that vitamin C may reduce the high levels of sorbitol found in diabetics. Sorbitol accumulation in retinal cells causes retinopathy which can lead to impaired vision which is a common problem for diabetics.
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