Sorry, chocoholics, dark chocolate doesn’t improve eyesight

If dark chocolate's myriad health benefits are how you justify having another piece at Halloween, then here's some bad news: better vision might not be one of those perks.

Published online Sept. 26 in JAMA Ophthalmology, a small-scale study challenged previously published research that found flavanol-rich dark chocolate may ever so slightly improve visual acuity and contrast sensitivity, countering that those changes couldn't be replicated either subjectively or objectively as measured by optical coherence tomography (OCT) angiography. These latest findings might not be to chocolate lovers' delight; however, it continues a conversation on the effects of flavonoids in ocular health.

Flavonoids, a large group of phytonutrients that give fruits and vegetables pigment, have been shown to have antioxidant, anti-inflammatory, antithrombotic, vasodilatory and antitumor effects. In particular, flavanol, the flavonoid found in highest concentrations among the cacao beans that make chocolate, may prove slightly beneficial to cardiovascular health. But not all chocolate gets that healthful rap.

Commercial confectionery processing cuts most of the bitterness from cacao beans—a bitterness attributed to those beneficial flavanols. As such, sweeter milk chocolate contains far less flavanol and white chocolate contains none as opposed to bitter dark chocolate. Even then, only dark chocolate with higher percentages of cacao solids (70% or more) contain more flavanols. These flavanol differences directly factored into German researchers' recent study, comparing the ocular effects of dark chocolate vs. milk chocolate ingestions.

The findings

Per the double-blind, randomized clinical crossover trial, researchers selected 22 healthy participants to consume either 20 g dark chocolate (400 mg of flavanols) or 7.5 g milk chocolate, then evaluated their visual function and retinal perfusion two hours later. Researchers noticed no differences in the effect of dark vs. milk chocolate on subjective visual acuity or contrast sensitivity, no change in retinal vessel density and no difference in arterial pressure as measured by OCT angiography.

The findings counter those of a 2018 study that reported a small improvement in visual function 105 minutes after consuming 72% cacao dark chocolate with 316.3 mg of flavanols. Although that previous study did note the effect was most likely of little clinical relevance.

"Despite administering a great amount of flavanol, in neither respect investigated was our small crossover trial able to demonstrate any effects of flavanol-rich dark chocolate on ocular function or anatomy, be it the primary objective end point of retinal perfusion in the central 3 mm and 6 mm of the posterior pole centered on the macula, both in the superficial and deep retinal plexus, or the secondary end points concerning subjective visual function, including ETDRS distance visual acuity or contrast sensitivity measured by both the established Pelli-Robson and Mars charts," authors of the most recent study note.

Although researchers did not find evidence of dark chocolate's effect on visual acuity or retinal blood flow, they did note that further trials with larger sample sizes may help rule out or in possible long-term benefits.

Nutrition and eye health

Prevailing research and dietary guidelines emphasize fruit and vegetable consumption to improve overall health, as well as directly reducing the risk of numerous chronic diseases. In fact, evidence suggests increasing just one serving of fruits and vegetables per day may help reduce the risk of coronary heart disease by 4%. So, too, adding certain nutrients to patients' daily diet—through healthy foods and supplementation—can also help preserve vision.

For instance, a 2018 study examined flavonoid intake using the 15-year follow-up Blue Mountains Eye Study. That research found an association between total flavonoid intake and 15-year incidence of AMD, concluding a serving of oranges (flavanone) daily could reduce risk of age-related macular degeneration (AMD) development by more than 60%. While no significant association was reported with flavonoid classes, flavanols or isoflavones, researchers posit flavonoids' powerful antioxidant effect could be the beneficial effect at work.

Currently, researchers believe AMD development is associated with depleted macular pigment, which filters light and reduces free radical development that causes cellular membrane oxidation. A diet rich in flavonoids and carotenoids may impart sufficient antioxidants to help eliminate these free radicals, in turn helping slow or prevent AMD progression. But those aren't the only nutrients beneficial to eye health.

Other studies, such as the Age-Related Eye Disease Studies (AREDS), sponsored by the National Eye Institute, have shown a link between eye health and nutrition. The AREDS studies found beneficial nutrients, including:

• Lutein and zeaxanthin
  Found in green leafy vegetables, these nutrients may help reduce the risk of AMD and cataracts.
• Vitamin E
  Found in nuts, cereals and sweet potatoes, this antioxidant may protect cells in the eye from free radical damage.
• Vitamin C
  Found in fruits and vegetables, this antioxidant may lower the risk for cataracts and slow AMD progression.
• Omega-3 Fatty Acids
  Found in fatty fish and other seafood, these healthy fats are important for proper visual development and retinal function.
• Zinc
  Found in red meat, seafood and chicken, this trace mineral concentrates in the retina and choroid and its deficiency is associated with poor night vision and possibly cataracts.

For more information about eye health and nutrition, access AOA's Diet & Nutrition page. To find educational and office materials, visit AOA Marketplace for nutritional resources, including "Essential Nutrients Your Eyes Need," "Feast Your Eyes-Nutrition and Eye Health Booklet," and the ocular supplement resources fact sheet.