The acute effect of cocoa and red-berries on visual acuity and cone-mediated dark adaptation in healthy eyes

Abstract

The retina is a highly vascularized tissue with a high metabolic and oxygen demand responsible for human vision. Considering that the polyphenolic flavanols and anthocyanins have been shown to be beneficial for endothelial function and cerebral blood-flow, an acute randomized and controlled crossover trial with two different sources of polyphenols, anthocyanins from red-berries and flavanols from cocoa, was designed to better understand the effect of polyphenols on visual acuity (VA) and cone-mediated dark adaptation (DA). Thirty-seven healthy subjects (22.1 ± 2.0 years old) participated in the acute intervention for three times (red-berries, cocoa or vehicle-control) with a washout period of two weeks in-between. VA under photopic and low luminance (mesopic) conditions, DA or dynamic of recovery of contrast threshold (CT) following near-total photopigment bleach for 5 min, urine total polyphenols, theobromine and antioxidant power were measured in the three study-arms after 2-hours ingestion of the study-food. 3-hours postprandial urine showed higher levels of total polyphenols after ingestion of cocoa flavanols or red-berries anthocyanins in comparison with the vehicle-control and higher levels of theobromine only for the cocoa group. There was an increase in photopic VA with cocoa flavanols that with red-berries anthocyanins did not reach statistical significance. Both, cocoa and red berries, failed to improve mesopic VA and the cone time constant for contrast recovery and final CT of DA.