Dark chocolate intake may improve vision
Eating dark chocolates may have short-term beneficial impacts on vision, according to a recent study, which reports significant improvements in contrast sensitivity and visual acuity following dark vs milk chocolate consumption.
Small-letter contrast sensitivity was significantly better in participants who consumed dark chocolates (mean score, 1.45±0.04 logCS) than those who were given milk chocolate (mean score, 1.30±0.05 logCS; mean improvement, 0.15 log CS; 95 percent CI, 0.08–0.22 logCS; p<0.001). [JAMA Ophthalmol 2018;doi:10.1001/jamaophthalmol.2018.0978]
Similarly, high-contrast visual acuity was also significantly better in participants who received dark (mean score, –0.22±0.01 logMAR) vs milk chocolate (mean score, –0.18±0.01 logMAR; mean improvement; 0.04 logMAR; 0.02–0.05 logMAR; p=0.05).
In contrast, while large-letter contrast sensitivity was higher after dark (mean score, 2.05±0.02 logCS) vs milk chocolate (mean score, 2.00±0.02 logCS) consumption, the difference in improvement was not statistically significant (mean improvement, 0.05 logCS; 0.00–0.10 logCS; p=0.07).
Combining all results from the tests, researchers showed that the composite scores indicated a significant overall improvement in spatial vision after dark vs milk chocolate consumption (mean improvement, 0.20 log U; 0.10–0.30 log U; p<0.001). However, the duration of these effects remains to be determined.
It has been shown in previous studies that dark chocolates, manufactured using flavonol-rich cacao beans, have beneficial effects on blood flow. This may explain the improvements observed in the present study, said researchers. [Front Immunol 2017;8:677]
“Although the specific mechanism for visual improvement awaits further study, an increase in retinal, visual pathway and/or cerebral blood flow could be contributory, enhancing bioavailability of oxygen and nutrients to metabolically active sites.” [Int J Cardiol 2009;131:424-429; Front Nutr 2017;4:43; Invest Ophthalmol Vis Sci 1994;35:646-648]
Moreover, dark chocolate has been reported as having positive effects on cardiovascular function, mood and cognition, and as being able to slow down degenerative diseases such as Alzheimer’s and Parkinson’s disease. The antioxidant effects of flavanols have been credited for such health benefits. [Front Immunol 2017;8:677]
“Dietary bioavailability of flavonoids is influenced by coingestion of other food products, susceptibility to oxidation and a short half-life, with plasma clearance occurring in as little as 4 hours. However, the exact duration of any improvement in vision performance was not determined in this study,” they added. [Front Nutr 2017;4:43]
The present randomized, single-masked, crossover study included 30 adults (mean age 26±5 years; 21 females) who had no pathologic eye diseases. All participants were asked to consume a dark or milk chocolate bar in separate sessions.
The primary study outcomes were within participant-comparisons for visual acuity, and large- and small-letter contrast sensitivity. Measurements were collected using binocular testing at 1.75 hours after the chocolate bars were consumed.
In summary, though the study findings showed improvements in visual acuity and large-letter contrast sensitivity, the effects were small and of unclear functional relevance, said researchers, however noting that the benefits of dark chocolate on small-letter contrast sensitivity, a more challenging visual task, was more pronounced.
“The highly vascularized retina, particularly the macula with its substantial projection to the visual cortex, may be most susceptible to enhanced blood flow and increased metabolic supply afforded by polyphenol flavanols in dark chocolate,” explained researchers. [J Cardiovasc Pharmacol 2006;47:S215-S220; Brain Res 2017;1672:50-57]