Scientists discovered that adults who ate a bar of dark chocolate saw a significant increase in visual clarity and contrast sensitivity in the 2 hours after consumption.
Study co-author Jeff C. Rabin, of the University of the Incarnate Word Rosenberg School of Optometry in San Antonio, TX, and team recently reported their findings in JAMA Ophthalmology.
Much to the delight of chocolate lovers, dark chocolate has started to develop a reputation as a health food, when consumed in moderation; it contains antioxidants called flavonoids, which are plant-derived compounds that can exert a number of positive effects, such as reducing inflammation.
It is believed that these flavonoids are largely responsible for some of the potential health benefits of dark chocolate consumption, which include better cognitive functioning and improved heart health.
Now, Rabin and colleagues suggest that the benefits of dark chocolate may extend to vision.
Visual acuity, contrast sensitivity improved
The researchers came to their findings by testing the effects of dark chocolate on the vision of 30 healthy adults — nine men and 21 women — who were an average age of 26 years. None of the subjects had a history of eye disease.
In two separate sessions, each participant was required to consume a small bar of dark chocolate containing 316.3 milligrams of flavanols — which are a class of flavonoids — or a small milk chocolate bar, containing just 40 milligrams of flavanols.
The trial was single-masked, meaning that the participants were not told which type of chocolate they were consuming at each session.
Approximately 2 hours after chocolate consumption, all subjects underwent visual testing.
The results revealed an improvement in visual contrast sensitivity — or the ability to read small and large letters at different contrasts — after subjects consumed dark chocolate, compared with when they consumed the milk chocolate.
Subjects also experienced a slight improvement in visual acuity — that is, the clarity of vision — after dark chocolate consumption.
However, the researchers note that it is unclear how long these visual improvements last. They write:
"The findings reported suggest that a single dose of dark chocolate improves visibility of small, low-contrast targets within 2 hours compared with milk chocolate, but the duration of this difference and clinical relevance remains uncertain."
Further research needed
While the study was unable to identify the reasons why dark chocolate intake may improve vision, the researchers propose some theories.
The authors say, "[...] an increase in retinal, visual pathway, and/or cerebral blood flow could be contributory, enhancing bioavailability of oxygen and nutrients to metabolically active sites."
The researchers also note a number of limitations to their study. For example, they concede that participants may have been aware of the type of chocolate they were consuming based on its taste, and this may have influenced the results.
In conclusion, the team believes that further studies are warranted to test the potential visual benefits of eating dark chocolate.