In theory, Vitamins C and E and magnesium could help prevent or limit diabetic retinopathy (DR), a potentially blinding disease, since each nutrient causes the body to respond in ways that alter retinopathy mechanisms. For example, in animal models Vitamins C and E suppress production of a growth factor, VEG-F, which can promote abnormal blood vessels in the retina. And high dietary levels of magnesium are associated with lower blood pressure and blood sugar, both of which correlate with a lower risk of retinopathy.
A research team led by Amanda Adler, MD, PhD, Institute of Metabolic Science, Cambridge, United Kingdom, surveyed studies published from 1988 through 2008 on the impact of these micronutrients on DR. Based on 15 selected studies comprising 4,094 individuals, Dr. Adler says to the evidence is not strong enough yet to recommend Vitamins C or E or magnesium supplements for patients with diabetes. She thinks the research should continue, though, and recommends specific parameters.
"It is a very attractive proposition that what one eats, rather than a medication, might reduce the risk of diabetic complications. Ideally, future studies would include frequent measurement of intake of these three nutrients through diet and supplements, standardized exams to identify DR, and agreed-upon biomarkers to assess DR progression," Dr. Adler said. "If such studies showed apparent protection against DR, then a randomized clinical trial could determine more precisely how a person with diabetes might, or might not, alter his intake of any of these nutrients," she said.
The Adler survey found that in hospital-based studies, participants with higher levels of Vitamin C in their blood were less likely to have DR, but in population-based studies there was no association between dietary intake of Vitamin C and DR. For Vitamin E, no studies showed an association between blood levels or dietary intake and DR risk. For magnesium, one study showed an association between low blood levels of magnesium and DR progression, but other studies were inconclusive.
This research was published in the January 2010 issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
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