Are dietary intake parameters of vitamin A, carotene, retinol appropriate factors to evaluate the risk of diabetic retinopathy?

{"Background": "Diabetic retinopathy (DR) is a leading cause of blindness in adults worldwide. Persistent hyperglycemia activates metabolic pathways and increases oxidative stress, suggesting antioxidants like vitamin A may play a protective role. Vitamin A occurs as retinol (animal sources) and carotene (plant sources). Previous studies on the association between vitamin A and DR have yielded conflicting results. The authors hypothesized that methodological differences\u2014particularly whether dietary intake or serum levels are measured\u2014may explain these discrepancies. This study aimed to determine whether dietary intake parameters of vitamin A, carotene, and retinol are sufficient to assess DR risk.", "Methods": "Data were from the Korean National Health and Nutrition Examination Survey (KNHANES) 2008-2012, a population-based cross-sectional study using stratified, multistage clustered sampling. Of 56,846 individuals, 1,948 subjects aged \u226540 years with diabetes and complete data were analyzed. Dietary intake was assessed via a single 24-hour recall administered by trained nutritionists, using the Food Composition Table (7th revision). Diabetes was defined by fasting glucose >126 mg/dL, random glucose >200 mg/dL, HbA1c >6.5%, or hypoglycemic medication use. DR was diagnosed from 7 standard fundus photographs after pupil dilation using the ETDRS severity scale. Logistic regression was used with three models: Crude (unadjusted), Model 1 (adjusted for age and sex), and Model 2 (adjusted for age, sex, hypertension, HbA1c, and diabetes duration).", "Key Results": "Participants with DR were older (61.4 vs. 59.5 years, P=.010), had higher systolic BP (130.9 vs. 127.5 mmHg, P=.015), longer diabetes duration (11.2 vs. 6.9 years, P<.001), higher HbA1c (8.04% vs. 7.19%, P<.001), and higher fasting glucose (157.4 vs. 139.5 mg/dL, P<.001). In crude analyses, the highest quartile of dietary vitamin A intake was associated with lower odds of any DR (OR 0.51, 95% CI 0.35-0.73, P for trend <.001), PDR (OR 0.40, 95% CI 0.18-0.88, P for trend=.046), and VTDR (OR 0.41, 95% CI 0.21-0.80, P for trend=.008). However, after full adjustment (Model 2), all associations became non-significant: any DR (OR 0.72, 95% CI 0.45-1.16, P for trend=.462), PDR (OR 0.46, 95% CI 0.17-1.26, P for trend=.320), VTDR (OR 0.49, 95% CI 0.20-1.20, P for trend=.150). Similarly, higher carotene intake showed crude protective associations for any DR (Q4 OR 0.50, 95% CI 0.34-0.72, P for trend <.001) that became non-significant after adjustment (Q4 OR 0.65, 95% CI 0.39-1.09, P for trend=.220). Higher retinol intake showed crude protection for any DR (Q4 OR 0.49, 95% CI 0.34-0.72, P for trend=.001) that disappeared after adjustment (Q4 OR 1.05, 95% CI 0.62-1.80, P for trend=.279).", "Clinical Implications": "Dietary intake parameters of vitamin A, carotene, and retinol are insufficient to assess DR risk. The authors argue that serum vitamin A levels are more accurate because dietary intake does not account for absorption variability (vitamin A is fat-soluble and absorption depends on digestive health), and a single 24-hour recall has inherent bias for micronutrient assessment. The authors note that previous studies showing protective associations may have inadequately adjusted for key confounders (HbA1c, diabetes duration, hypertension). They report unpublished data from 11,727 subjects showing that serum vitamin A levels had an inverse relationship with DR (OR 0.3 for any DR after adjustment), supporting their conclusion that serum measures are more appropriate. Major limitations include the cross-sectional design (cannot infer causality), potential selection bias from non-mandatory exams, and reliance on a single 24-hour dietary recall."}