Vitamin E,diabetes and related diseases: an update

Abstract

Natural vitamin E is a mixture of tocopherols and tocotrienols synthesized only by plants. It is very difficult to determine the optimal dietary intake of vitamin E, but there is a general agreement indicating a level of 8 mg/day (12–15 IU). This value seems to be sufficient only to prevent deficiency syndromes of vitamin E. In humans, vitamin E is absorbed together with nutritional lipids in the proximal part of the intestine and released in the lymph within chylomicrons. Vitamin E supplementation, as other minerals and vitamins, is able to participate in the decrease of oxidative stress in diabetic patients by improving glycemic control and/or by other mechanisms related to its antioxidant activity, therefore cooperating to the control of diabetic complications. Many interventional trials evaluating the effect of antioxidant supplementation on insulin resistance, plasma glucose levels and risk of T2D give inconsistent results. At present, a controversial hypothesis about the role played by vitamin E supplementation still exists. In fact, while laboratory data report great cellular and biochemical beneficial actions, clinical trials have failed to support these claims. Concerning clinical trials, the discrepancies have been attributed to differences in selection of individuals, dosage, chemical forms of vitamin E, duration of treatment, stage of the disease and geographical area. Because of these variables, further studies aimed to clarify the relationship between diabetes, cardiovascular risk factors and vitamin E are necessary.