Research Articles in Diabetes and Diabetic
Retinopathy
Antioxidant Nutrient Intake and Diabetic Retinopathy: The San Luis
Valley Diabetes Study
(From Ophthalmology 1998;105:2264-2270, Mayer-Davis EJ, PhD, Et al.)
OVERVIEW:
This study evaluates any possible association between intake of antioxidant nutrients
(specifically, Vitamins C, E, and Beta-Carotene) and the risk of diabetic retinopathy. The
antioxidant nutrients were present either in the diets of the individuals, or were taken
as supplements. The taking of the supplements, and the diets of the study subjects, were
up to the individuals themselves, without interference from the authors of the study. The
San Luis Valley Diabetes Study is an epidemiologic study looking at the natural history of
Type 2 diabetes mellitus in a biethnic community (approximately 2/3 Hispanic). The dietary
assessments were taken as a 24-hour recall interview during a clinic visit. Follow-up eye
examinations ranged up to 6 years. The analysis accounted for age, duration of diabetes,
insulin use, ethnicity, glycated hemoglobin, hypertension, gender, and caloric intake.
There were a total of 387 participants in this study.
RESULTS:
At baseline, approximately 22% of the participants had background diabetic retinopathy,
10% had preproliferative retinopathy, and 4% had proliferative retinopathy. Those with
severe retinopathy had a longer duration of diabetes and were more likely to be taking
insulin. Glycated hemoglobin levels (HbA1c) were the lowest in those with no retinopathy.
In general, individuals with no diabetic retinopathy had lower levels of antioxidant
intake compared to those with background or severe retinopathy. No individuals took
supplements of Beta-Carotene, so levels of intake were based on dietary history.
Specifically, for each antioxidant studied:
-
Vitamin C:
-
Vitamin E:
-
Increased intake of Vitamin E was associated with increased severity of diabetic
retinopathy among those not taking insulin.
-
While previous studies have shown that supplemental Vitamin E decreases glycosylated
hemoglobin levels, this study showed no association between Vitamin E intake in older
adults with diabetes and HbA1c levels.
-
Vitamin E supplementation was not associated with reduced prevalence or severity of
diabetic retinopathy.
-
Beta-Carotene:
-
Among those taking insulin, intake of Beta-Carotene was not found to be associated with
reduced prevalence or severity of diabetic retinopathy.
-
No actual supplementation of Beta-Carotene was reported by the subjects, only dietary
consumption. High-dose supplementation of Beta-Carotene has been related to increased risk
of coronary heart disease and death (Omenn GS, et al. Effects of a combination of
beta carotene and vitamin A on lung cancer and cardiovascular disease. New England Journal
of Medicine 1996;334:1150-1155.)
CONCLUSIONS:
The authors admit that determination of the dietary intake of antioxidants may not be
completely accurately measured by the 24-hour recalls. Serum levels of antioxidants were
not available for analysis. Overall, this study shows no protective effect of the
antioxidants Vitamin C, E, and Beta-Carotene on the prevalence and severity of diabetic
retinopathy in Type 2 diabetics in a biethnic population. Further investigation of this
issue is warranted, especially with possible risk of worsening retinopathy.
For information about diabetic eye disease in general, and
for an explanation of terminology used below, go to
Diabetic Eye Disease.
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