Caffeine, Dairy Products and Common Aspects of Dietary Intake Are Associated with Functional and Structural Alterations in Retinal Microcirculation: A Systematic Review

Background: Caffeine, dairy products and other food items may influence retinal microcirculation. Retinal microvascular indices provide quantitative biomarkers of systemic microvascular health and are increasingly used in clinical and research settings. The aim of this study was to elucidate the possible effects of these food products on structural and functional indices of the retinal microcirculation. Methods: Based on a registered protocol, we identified eligible interventional/observational studies examining the association of these factors with retinal biomarkers, including central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), arteriolar-to-venular diameter ratio (AVR), retinal vascular tortuosity, vessel diameter index (VDI) and retinal vessel flicker light-induced dilation (FID). Results: Fourteen studies were included addressing caffeine (4), dairy products (2) and other food (9) consumption. Acutely, caffeine intake was dose-dependently associated with narrowed CRAE, CRVE, decreased VDI and increased AVR and FID. Long-term, caffeine consumption was associated with larger CRVE and lower AVR, while decaffeinated coffee with larger CRAE and AVR and narrower CRVE. Low-fat dairy products, fish and fiber were associated with larger CRAE, smaller CRVE, and increased AVR, while red meat consumption was associated with narrower CRAE and lower AVR. Increased salt intake was associated with increased venular tortuosity, while almond consumption was associated with larger CRVE. Owing to substantial study heterogeneity, a meta-analysis was not feasible. Conclusions: Potentially clinically meaningful associations between food groups and retinal indices were identified. These associations should be considered when evaluating retinal microcirculation and assessing CVD risk since modification of these factors may be beneficial for the cardiovascular system.