Micronutrients and Diabetic Retinopathy A Systematic Review

Background: We have evaluated the evidence for the association between intake and blood levels of micronutrients and diabetic retinopathy. Treatment for diabetic retinopathy requires significant clinical input and specialist ophthalmologic care. Micronutrients, including vitamin C, vitamin E, and magnesium, may interfere with pathologic mechanisms of diabetic retinopathy and potentially alter its risk. Methods: We conducted a search of epidemiologic literature in PubMed and Embase from 1988 to May 2008, using keywords for exposures, including magnesium, ascorbic acid, alpha-tocopherol and antioxidants, and outcomes, including diabetic retinopathy. Two authors independently extracted data and assessed the quality of the studies using the Newcastle-Ottawa Scale. The overall quality of evidence was graded as I ( highest), II, or III ( lowest). Results: Of the 766 studies identified, we reviewed 15 studies, comprising 4094 individuals. For vitamin C, hospital-based studies reported an inverse association between plasma levels with retinopathy, whereas population-based studies showed no association between dietary intake and retinopathy. For vitamin E, there was no association with dietary intake or plasma levels and retinopathy. For magnesium, a single prospective analysis showed an association between low levels in plasma and progression of retinopathy, but cross-sectional studies reported inconsistent results. In the assessment of quality, population-based studies had higher ratings than hospital-based studies. Conclusions: The evidence suggests that dietary intake or plasma levels of vitamins C and E and magnesium do not seem to be associated with diabetic retinopathy. Because of differences in study designs and measurement of micronutrients, incomplete ascertainment of retinopathy, and residual confounding, these findings require confirmation.