**Background:** Diabetic retinopathy (DR) is a leading cause of vision loss in people with diabetes. Nutritional therapy may help prevent diabetic complications, but the relationship between caffeine intake and DR risk is unclear, with conflicting evidence from prior studies. This study aimed to assess the association between caffeine intake (including food sources) and DR in subjects with type 2 diabetes (T2D) without other late diabetic complications, and to test the effect of topical caffeine in an experimental diabetic mouse model.
**Methods:** The clinical study was a cross-sectional analysis of 291 subjects with T2D (144 with DR, 147 without DR) recruited from a DR screening program in Catalonia, Spain, from March 2010 to January 2013. Participants were aged 40–75 years. Exclusion criteria included other advanced diabetes complications (macroalbuminuria, renal failure, prior cardiovascular disease) and conditions affecting clinical/nutritional variables. Caffeine intake was assessed using a validated 101-item semiquantitative food frequency questionnaire (FFQ). Caffeine sources included coffee (89.5% of intake), light soft drinks (6.72%), soft drinks (1.56%), tea/infusions (0.87%), and others. Nutrient intakes were energy-adjusted using the residual method. DR was classified by an experienced ophthalmologist using the international clinical classification system. Multivariable logistic regression models adjusted for age, sex, educational level, physical activity, hypertension, dyslipidemia, diabetes duration, HbA1c, BMI, and tobacco exposure. For the experimental study, 20 male db/db diabetic mice and 10 non-diabetic db/+ controls were used. Caffeine eye drops (5 mg/mL) or vehicle were administered topically twice daily for two weeks to 10-week-old diabetic mice. Glial activation was assessed by GFAP immunofluorescence scoring, and vascular leakage was measured using the Evans Blue albumin method.
**Key Results:** Subjects with DR were older (60.4 vs. 57.9 years, p=0.024), had longer diabetes duration (14.0 vs. 7.07 years, p<0.001), higher HbA1c (8.2% vs. 7.3%, p<0.001), higher systolic blood pressure (145 vs. 134 mmHg, p<0.001), and higher prevalence of hypertension (66.7% vs. 49.7%, p=0.005) compared to those without DR. In the bivariable analysis, the second (Q2: 0.11–1.08 g/day) and fourth (Q4: 3.11–9.55 g/day) quartiles of caffeine intake were associated with lower odds of DR (OR 0.46, 95% CI 0.24–0.90, p=0.022; and OR 0.47, 95% CI 0.24–0.92, p=0.027, respectively) compared to the lowest quartile (Q1: 0.00–0.10 g/day). In the fully adjusted multivariable model, Q2 and Q4 remained significantly protective (OR 0.35, 95% CI 0.16–0.78, p=0.011; and OR 0.35, 95% CI 0.16–0.77, p=0.010, respectively), representing a 65% reduced risk. However, caffeine intake as a continuous variable was not significantly associated with DR (OR 0.93, 95% CI 0.81–1.05, p=0.241). No significant association was found between coffee/tea consumption (continuous or quartiles) and DR. Hypertension (OR 2.16, 95% CI 1.17–4.05, p=0.014), diabetes duration (OR 1.11, 95% CI 1.06–1.16, p<0.001), and HbA1c (OR 1.60, 95% CI 1.28–2.03, p<0.001) were significant risk factors. In the experimental study, diabetic mice treated with vehicle showed significantly higher GFAP expression than non-diabetic controls (p<0.01), indicating glial activation. Caffeine eye drops did not significantly reduce reactive gliosis or vascular extravasations compared to vehicle.
**Clinical Implications:** This study suggests that moderate to high daily caffeine intake may be associated with a substantially lower risk of diabetic retinopathy in adults with type 2 diabetes without other advanced complications. However, the lack of a linear dose-response relationship and the null findings for coffee/tea consumption specifically, along with negative experimental results, indicate that the protective effect may not be directly attributable to caffeine itself but possibly to other bioactive compounds (e.g., chlorogenic acid, flavonoids) in caffeinated beverages. The cross-sectional design precludes causal inference, and the small sample size limits statistical power. These findings highlight the need for prospective studies and clinical trials to clarify the role of caffeine and other coffee/tea constituents in DR prevention.