Research Roundup: How That Morning Coffee Affects Your Patients’ Ocular Health

A theory on motivation suggests that humans are driven by 4 general concepts: money, ideology, compromise, and ego. But, perhaps an overlooked source of daily inspiration, the reason many get out of bed in the morning, is coffee. Yes, our daily grounds get many of us through the daily grind, but as with anything taken so habitually, physicians and researchers are curious to know its health effects. In ophthalmic care, technologies such as optical coherence tomography (OCT) and its many applications can provide data on structural layers deep within the eye. And so, investigators have used these new options to review the potential effects the stimulant can have on ocular health. What they’re finding is that a lot of old notions about coffee’s risks are unfounded, and that a morning cup of Joe is actually more closely associated with health benefits.

Here, we provide an overview of what the latest research says, and how ophthalmology patients should take their coffee.

Systemic Effect of Coffee 

Caffeine may have a bad rap. While it may have addictive qualities, studies also demonstrate that daily caffeine intake has a number of bona fide health benefits as well. Researchers highlight some of these benefits in an analysis of 3 large trials published in the American Heart Association’s journal Circulation: Heart Failure.¹ They found the more coffee people drank, the lower their risk for heart failure — with participants who drank 2 or more cups a day experiencing an approximate 30% lower risk than those who did not drink coffee or people who drank decaf.¹ Additionally, coffee drinkers appear to have a reduced risk of type 2 diabetes and it can even be protective against liver disease.^2,3 In fact, investigators have even reconsidered  some conditions previously associated with caffeine intake. Breast cancer, for example, was once thought to be linked to daily coffee consumption. However, later studies show that coffee drinkers actually have fewer incidences of breast cancer, especially among patients who are postmenopausal.^4-6 Of course, all that research is quantified with specific amounts of coffee and doesn’t take into account the many sugar-laced add-ons folks order at their local chains. 

In eye care, the question of coffee’s influence has also been percolating in researchers’ minds. Can patients with age-related macular degeneration safely enjoy a morning brew? How does caffeine affect the ocular surface? Which patients would benefit from avoiding caffeine?

Rethinking Caffeine’s Effect on Dry Eye 

Plenty of prior reporting speculates that coffee’s diuretic quality has the potential to cause further damage to already dry eyes.^7,8 However, recent direct investigations into the relationship between caffeine and dry eye suggests that the stimulant does not have any such effect on the ocular surface.^9,10 In fact, some research has linked increased coffee consumption with stimulating tear production.^8,10-12 

Coffee was most recently ruled out as a factor in dry eye development in a 2022 investigation published in Cornea that considered 85,302 participants (mean age 50.7 years, 59% women).⁹ Participants in the Netherlands were evaluated using the Women’s Health Study dry eye questionnaire. That research looked at dietary caffeine in the form of coffee, tea, soda, and energy drinks. The mean daily intake of caffeine was estimated at 285±182 mg.⁹ After correcting for demographics, smoking status, alcohol use, and all other comorbidities, the study shows:

“Despite a mildly increased risk of highly symptomatic dry eye after adjusting for many comorbidities, increasing caffeine intake was still found to slightly reduce the risk of having a dry eye disease diagnosis,” indicating that no increased risk of dry eye, as defined by the Women’s Health Study, was found. “Discouraging caffeine intake in patients with dry eye disease on a general basis is not recommended.”⁹

The Management and Therapy Report chapter from the Tear Film & Ocular Surface Society’s (TFOS) Dry Eye Workshop II (DEWS II) also backs the findings of a 2014 study that shows Schirmer tests scores were higher than baseline scores 45 minutes and 90 minutes after caffeine consumption, indicating an increase in tear production following intake. That study evaluated participants by exposing them to 5.0 mg of caffeine per kg of body weight dissolved into 200 mL of water on their first visit, and exposing a second group to only 200 mL of water. On a second visit, the order of treatment was reversed and at each visit, Schirmer scores were measured at 45, 90, 135, and 180 minutes after treatment. (As an additional finding, that study shows that drinking water is not necessarily linked with any improvement in dry eye signs or symptoms).^12,13

Macular Findings in Coffee Drinkers

“Caffeine is endowed with anti-inflammatory and antioxidant properties, as reported by several studies on different models of neurodegenerative diseases, including Parkinson disease and Alzheimer disease,” according to a January 2022 report published in Frontiers in Pharmacology.¹⁴ In that study, researchers explored potential protective effects these properties might have in retinal tissues. What they found is that caffeine can potentially slow the progression of inflammatory retinal diseases such as age-related macular degeneration and diabetic retinopathy. Specifically, the researchers say that caffeine suppresses the lipopolysaccharide-induced inflammatory response behind retinal inflammation. It also was shown to reduce the expression of several inflammatory mediators in various cell types in mice. 

“Several studies demonstrated that some retinal diseases, such as AMD, are characterized by the abnormal expression and irregular distribution of tight junction proteins in retinal pigment epithelial (RPE) cells,” the researchers explain. Their research shows that caffeine actually protects RPE cells through the upregulation of brain-derived neurotrophic factor, a mechanism similar to the way it protects against Parkinson and Alzheimer disease.¹⁴

Some research suggests that coffee can even be protective against worsening ocular effects of diabetes. A Korean study that reviewed 37,753 participants shows that those with type 2 diabetes (n=1350) who drink more than 2 cups of coffee every day, had lower odds of having any diabetic retinopathy (OR 0.53; 95% CI 0.28-0.99) or vision-threatening diabetic retinopathy (OR 0.30; 95% CI 0.10-0.91) than those who drank less of it.¹⁵ 

“The thermogenic, antioxidative, and anti-inflammatory effects of coffee consumption were all suggested as possible mechanisms behind this association,” according to the researchers.¹⁵

Coffee’s Effect on Intraocular Pressure 

Caffeine has been shown to elevate the intraocular pressure (IOP), but there’s a nuance to that. The elevation is transient.¹⁶ Caffeine has a half life of approximately 5 hours (range  1.5-9.5 hours).¹⁷ This may inform clinicians about findings at a particular in-office visit, but it does not provide a complete picture of the patient’s IOP. In fact, habitual coffee drinkers may experience a reduction in IOP, and may even be less likely to develop glaucoma at all.^18-20 One research team suggested that the reason for that is because caffeine raises both ocular perfusion pressure and IOP together, “leading to no net effect on overall optic nerve perfusion.”¹⁹

A 2021 report from the Modifiable Risk Factors for Glaucoma Collaboration research group shows that regular caffeine consumption is associated with lower IOP, although that association was weak, according to the researchers. Those investigators also called the link between caffeine consumption and glaucoma “null.” Only when they factored in genetic predisposition to elevated IOP, was greater caffeine consumption associated with higher glaucoma prevalence, according to that report.¹⁹

A large study out of Japan took into account the frequency of coffee consumption for 9850 individuals. It found that participants who drank coffee more often (3 or more times daily) had significantly lower IOPs (by 0.4 mm Hg; 95% CI; range 0.2-0.5 mm Hg lower; P <.001) than those who only consumed coffee once a day.²⁰ 

Although that study found a slightly lower IOP in people without glaucoma, like the report from the Modifiable Risk Factors for Glaucoma Collaboration, it shows no decrease in the risk of developing glaucoma based on coffee consumption.^18,20

Holistic Advice 

Although much of this research touts the benefits of more coffee, overconsumption can still lead to systemic problems. For example, it can interrupt sleep.²¹ But even long held beliefs (such as coffee’s connection to ulcers and other stomach problems) are being re-evaluated.²² That can have a large impact when the product in question is being used habitually by up to 76% of the population.²³ As researchers elucidate more from investigations into the microvasculature and across broad swaths of the population, clinicians can offer better holistic guidance about specific lifestyle choices. 

References 

1. Stevens LM, Linstead E, Hall JL, Kao DP. Association between coffee intake and incident heart failure risk. Circulation: Heart Failure. 2021;14(2):e006799. doi:10.1161/CIRCHEARTFAILURE.119.006799 
2. Kolb H, Martin S, Kempf K. Coffee and lower risk of type 2 diabetes: arguments for a causal relationship. Nutrients. 2021;13(4):1144. doi:10.3390/nu13041144
3. Heath RD, Brahmbhatt M, Tahan AC, Ibdah JA, Tahan V. Coffee: The magical bean for liver diseases. World J Hepatol. 2017;9(15):689-696. doi:10.4254/wjh.v9.i15.689
4. Ishitani K, Lin J, Manson JE, et al. Caffeine consumption and the risk of breast cancer in a large prospective cohort of women. Arch Intern Med. 2008;168(18):2022-2031. doi:10.1001/archinte.168.18.2022
5. Ganmaa D, Willett W, Li TY. Coffee, tea, caffeine, and risk of breast cancer: a twenty two-year follow-up. Int J Cancer. 2008;122(9):2071–2076. doi:10.1002/ijc.23336
6. Lafranconi A, Micek A, De Paoli P, et al. Coffee intake decreases risk of postmenopausal breast cancer: a dose-response meta-analysis on prospective cohort studies. Nutrients. 2018;10(2):112. doi:10.3390/nu10020112
7. Griffin RJ, Griffin J. Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet. 2003;16(6):411-20. doi:​​10.1046/j.1365-277x.2003.00477.x
8. Moss SE, Klein R, Klein BE. Prevalence of and risk factors for dry eye syndrome. Arch Ophthalmol. 2000;118(9):1264-8. doi:10.1001/archopht.118.9.1264
9. Magno MS, Utheim TP, Morthen MK, et al. The relationship between caffeine intake and dry eye disease. Cornea. Published online January 26, 2022. doi:10.1097/ICO.0000000000002979
10. Relationship between dry eye syndrome and frequency of coffee consumption in Korean adults: Korea national health and nutrition examination survey v, 2010–2012. Korean J Fam Med. 2018;39(5):290-294. doi:10.4082/kjfm.17.0047
11. Arita R, Yanagi Y, Honda N, et al. Caffeine increases tear volume depending on polymorphisms within the adenosine A2a receptor gene and cytochrome P450 1A2. Randomized Controlled Trial Ophthalmology. 2012;119(5):972-8. doi:10.1016/j.ophtha.2011.11.033.
12. Osei KA, Ovenseri-Ogbomo G, Kyei S, Ntodie M. The effect of caffeine on tear secretion. Optom Vis Sci. 2014;91(2):171-177. doi:10.1097/OPX.0000000000000129
13. Jones L, Downie L, Korb D, et al. TFOS DEWS II management and therapy report. Ocul Surf. 2017;15(3):575-628. doi:10.1016/j.jtos.2017.05.006
14. Lazzara F, Romano GL, Platania CBM, Drago F, Bucolo C. Caffeine protects against retinal inflammation. Front Pharmacol. January 6, 2022. doi:10.3389/fphar.2021.824885
15. Lee J, Park J, Kwon S, et al. Coffee consumption and diabetic retinopathy in adults with diabetes mellitus. Nature Scientific Reports. Published online March 3, 2022. doi:10.1038/s41598-022-07192-6
16. Fahmideh F,  Marchesi N, Barbieri A, Govoni S, Pascale A. Non-drug interventions in glaucoma: Putative roles for lifestyle, diet and nutritional supplements. Surv Ophthalmol. Published online September 23, 2021. doi:10.1016/j.survophthal.2021.09.002 
17. Caffeine for the sustainment of mental task performance: formulations for military operations. Washington (DC): National Academies Press (US); 2001.
18. Kim J, Aschard H, Kang JH, for the Modifiable Risk Factors for Glaucoma Collaboration. Intraocular pressure, glaucoma, and dietary caffeine consumption. a gene-diet interaction study from the UK biobank. Ophthalmol. 2021;128(6):866-876. doi:10.1016/j.ophtha.2020.12.009
19. Fahmideh F, Marchesi N, Barbieri A, Govoni S, Pascale A. Non-drug interventions in glaucoma: putative roles for lifestyle, diet and nutritional supplements. Surv Ophthalmol. Published online September 23, 2021 doi:10.1016/j.survophthal.2021.09.002
20. Nakano E, Miyake M, Hosada Y, et al. Relationship between intraocular pressure and coffee consumption in a Japanese population without glaucoma: the Nagahama study. Ophthalmol Glaucoma. 2021;4(3):268-276. doi:10.1016/j.ogla.2020.09.019
21. O’Callaghan F, Muurlink O, Reid N. Effects of caffeine on sleep quality and daytime functioning. Risk Manag Healthc Policy. 2018;11(12):263–271. doi:10.2147/RMHP.S156404
22. Shimamoto T, Yamamichi N, Kodashima S. No association of coffee consumption with gastric ulcer, duodenal ulcer, reflux esophagitis, and non-erosive reflux disease: a cross-sectional study of 8,013 healthy subjects in Japan. PLoS One. Published online June 12, 2013. doi:10.1371/journal.pone.0065996
23. The National Coffee Data Trends Market Research Series – the “Atlas of American Coffee.” https://www.ncausa.org/Research-Trends/Market-Research/NCDT. Updated March 15, 2021. Accessed March 28, 2022.