Nutritional Benefits of Dietary Lutein, Zeaxanthin, and Meso-Zeaxanthin in Canine, Feline, and Equine Companion Animals: A Narrative Review

The macular xanthophyll carotenoids lutein, zeaxanthin, and meso-zeaxanthin have well-established roles in oxidative regulation, inflammation, and visual function in humans. Collectively, these carotenoids are perhaps best known for their ability to reduce the risk of development and progression of age-related macular degeneration in humans—a condition that resembles senile retinal atrophy in older dogs and cats, although the relevance of macular xanthophylls to companion animal health remains incompletely defined. This review synthesizes the available literature on the absorption, target tissue deposition, mechanistic pathways, and physiological effects of these carotenoids in dogs, cats, and horses. Evidence indicates that lutein and zeaxanthin, are absorbed and systemically distributed in companion animals, with the most robust functional data currently available in dogs, particularly regarding immune modulation and retinal electrophysiological stability. Carotenoid transport mechanisms, including high-density lipoproteins, binding proteins, such as scavenger receptor BI (SR-BI), transmembrane glycoprotein CD36, START-domain lipid-binding protein 3 (StARD3), and glutathione S-transferase pi 1 (GSTP1), and metabolic enzymes, including the carotenoid cleavage enzymes beta-carotene oxygenase 1 and 2 (BCO1 and BCO2), are conserved across mammalian species and provide a mechanistic framework for tissue- and system-specific activity in the visual, immune, nervous, integumentary, and cardiovascular systems among. Histologic confirmation remains limited, however, especially in cats and horses. Collectively, existing data suggest an important biological role for these xanthophyll carotenoids in companion animals, but substantial knowledge gaps remain regarding species-specific bioavailability, tissue deposition, and clinical outcomes. The biological benefits of lutein, zeaxanthin and meso-zeaxanthin in humans, along with the central similarities in mammalian physiology, support the potential of these dietary and supplemental compounds to enhance the health of companion animals. Future supplementation studies, however, are needed to characterize dose–response relationships in these species and clarify the potential functional benefits of these nutrients in companion animal nutrition.