Rumour has it that the Specsavers Clinical Conferences are flooded with coffee cups and chocolate wrappers stating that both coffee and chocolate is good for your eyesight. A quick search on the web returns thousands of web pages with the same information. We will examine the science behind this and see if adding chocolate or coffee to your diet should be a clinical recommendation.
We know from the Age-Related Eye Disease studies that adding high-concentration vitamin C, E and beta-carotene supplements might slow development of age-related macular degeneration, albeit for those with intermediate stage age-related macular degeneration (AMD)1,2. So, dietary supplements with antioxidants can be good for the eye health of some patients, but what does research tell us about chocolate and coffee?
Visual acuity and dark chocolate
A recent 2018 paper3 showed that participants had significantly increased visual acuity and contrast sensitivity two hours after consumption of dark chocolate, compared to milk chocolate. However, there were only 30 participants in this study, and both investigators and participants could be biased and unknowingly have affected the study outcome.
Also, the use of “significantly” indicates a statistically significant finding, not necessarily a huge difference. For this study, visual acuity increased from -0.15 logMAR (approx. Snellen 6/4.2 or 1.41) for milk chocolate too -0.22 logMAR (approx. Snellen 6/3.6 or 1.66) for dark chocolate. Or, about a four-letter improvement on the logMAR chart.
What about a cup of joe?
For coffee, there are no studies that examine coffee itself as an intervention in humans, but there are studies looking at animal models and the effect on cells, as well as cross-sectional studies looking at coffee consumption and associated lifestyle factors and diseases. Singling out coffee as a cause or protective factor to diseases can’t be done from these studies. And, given the high coffee consumption in the world, designing a study that can give definitive answers two the effect of normal coffee consumption can be challenging.
Dietary supplements and AMD
However, we do know that high-dose dietary supplements can be beneficial to persons with AMD. This has been shown by the Age-Related Eye Disease Study1 and Age-Related Eye Disease Study 22 (AREDS and AREDS2). The results from these studies have cumulated in multiple eye-specific high-dose dietary supplements which are available over the counter. One might be tempted to provide these to AMD patients, hoping that it will slow the progression of the disease. However, it’s important to remember that they are only shown to be beneficial to AMD patients with moderate or advanced dry AMD, particularly patients with intermediate size drusen, one or more large drusen or non-central geographic atrophy in one or both eyes1,2,4,5. And the addition of lutein and zeaxanthin have little or no effect on the progression of AMD2,4,5.
Advice to customers
Although we, unfortunately, can’t make a clinical recommendation to have a high coffee or chocolate diet, we can advise our patients and customers that a healthy lifestyle with a diverse diet including green-leaf vegetables, grain and fish is the best. But be aware that diets high in green vegetables (e.g. broccoli, spinach, kale, etc.) contain high levels of vitamin K, which can inhibit the effect of blood thinning medications6. Also, be aware that high levels of beta-carotene can increase the risk of lung cancer in smokers. Since dietary supplements can be both beneficial and harmful, it’s important to advise the use of them in cooperation with our customers’ or patients’ medical physician.
But please enjoy both coffee and chocolate in moderate amounts – and enjoy all learnings you get from the Green Club and Specsavers Clinical Conference.
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- Age-Related Eye Disease Study Research Group. A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation With Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss: AREDS Report No. 8. Arch Ophthalmol. 2001;119(10):1417–1436. doi:10.1001/archopht.119.10.1417
- The Age-Related Eye Disease Study 2 (AREDS2) Research Group. Lutein + Zeaxanthin and Omega-3 Fatty Acids for Age-Related Macular Degeneration: The Age-Related Eye Disease Study 2 (AREDS2) Randomized Clinical Trial. JAMA. 2013;309(19):2005–2015. doi:10.1001/jama.2013.4997
- Rabin JC, Karunathilake N, Patrizi K. Effects of Milk vs Dark Chocolate Consumption on Visual Acuity and Contrast Sensitivity Within 2 Hours: A Randomized Clinical Trial. JAMA Ophthalmol. 2018;136(6):678–681. doi:10.1001/jamaophthalmol.2018.0978
- Arroyo JG. Age-related macular degeneration: Treatment and prevention. In Trobe J & Schmader KE (Ed.). UpToDate. 2018. Retrieved 2018-10-01, from https://www.uptodate.com/contents/age-related-macular-degeneration-treatment-and-prevention#H3
- Evans JR, Lawrenson JG. Antioxidant vitamin and mineral supplements for slowing the progression of age‐related macular degeneration. Cochrane Database of Systematic Reviews 2017, Issue 7. Art. No.: CD000254. DOI: 10.1002/14651858.CD000254.pub4.
- Hull RD, Garcia DA & Vazquez SR. Warfarin and other VKAs: Dosing and adverse effects. In Leung LLK (Ed.). UpToDate. 2018. Retrieved 2018-10-01, from https://www.uptodate.com/contents/warfarin-and-other-vkas-dosing-and-adverse-effects#H23
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