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Original Investigation
September 26, 2019

Effects of Flavanol-Rich Dark Chocolate on Visual Function and Retinal Perfusion Measured With Optical Coherence Tomography Angiography: A Randomized Clinical Trial

Author Affiliations
  • 1Department of Ophthalmology, Ludwig-Maximilians-University, Munich, Germany
JAMA Ophthalmol. Published online September 26, 2019. doi:10.1001/jamaophthalmol.2019.3731
Key Points

Question  Does flavanol consumption in dark chocolate improve visual acuity, contrast sensitivity, or retinal perfusion on optical coherence tomography angiography as suggested previously?

Findings  In a double-blind randomized clinical crossover trial, 22 participants were randomized to consume flavanol-rich dark and regular milk chocolate. Dark chocolate was not shown to increase visual acuity, contrast sensitivity, or retinal perfusion on optical coherence tomography angiography compared with milk chocolate ingestion.

Meaning  In contrast to a previous trial reporting beneficial effects of dark chocolate flavanol on visual function, this similarly sized trial did not find any effects on subjective (visual function) or objective (retinal perfusion) end points.


Importance  A recently reported randomized clinical trial suggested beneficial effects of vasodilating flavanols in dark chocolate on visual function without objective quantification of retinal perfusion.

Objective  To assess the effects of dark chocolate flavanols on subjective visual function and retinal perfusion objectively quantified on optical coherence tomography (OCT) angiography.

Design, Setting, and Participants  This randomized, masked double-blind crossover clinical trial analyzed 22 healthy participants at the Department of Ophthalmology, Ludwig Maximilians-University Munich, Germany, in July 2018. Analysis was intention to treat. Analysis began in July 2018.

Interventions  Participants were randomized to consume 20 g of dark chocolate containing 400 mg of flavanols or 7.5 g of milk chocolate. Two hours later, visual function and retinal perfusion on OCT angiography were evaluated. Systemic blood pressure was measured to rule out artifacts on OCT angiography.

Main Outcomes and Measures  The primary end point was macular retinal perfusion quantified as vessel density on OCT angiography. The secondary end point was subjective visual function (Early Treatment Diabetic Retinopathy Study visual acuity, Pelli-Robson chart, and Mars chart contrast sensitivity).

Results  All 22 participants (13 women [59.1%]; mean [SD] age, 27.3 [11.1] years) completed the trial. No relevant differences in baseline parameters between groups were identified. No change in the primary outcome measure, retinal perfusion, could be detected after consumption of dark vs milk chocolate (superficial plexus 48.0% vs 47.5%, treatment effect: −0.59 [95% CI, −2.68 to 1.50], P = .56; deep plexus 54.1% vs 54.0%, treatment effect: −1.14 [95% CI, −4.01 to 1.73], P = .42). No differences in changes in the secondary outcome parameters Early Treatment Diabetic Retinopathy Study visual acuity, Pelli-Robson chart, or Mars chart contrast sensitivity could be detected. Potentially confounding effects of changes in blood pressure were excluded.

Conclusions and Relevance  In contrast to a previous similarly sized randomized clinical trial reporting beneficial effects on visual function, no short-term effects of flavanol-rich dark chocolate on automatically assessed retinal blood flow on OCT angiography or subjective visual function were observed in this study. As this small trial does not rule out the possibility of benefits, further trials with larger sample sizes would be needed to rule in or out possible long-term benefits confidently.

Trial Registration  German Clinical Trials Register identifier: DRKS0001506

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