We view ourselves as the gatekeepers for our patient’s health, as well as health educators. When we make a diagnosis of glaucoma or glaucoma suspect, in addition to learning about the medical management of that ocular disease, our patients inevitably want to know what they can do to reduce their risk of diagnosis or progression of disease.
This article will focus on the latest medical research on foods, vitamins, and supplements that may have an effect on glaucoma. This will help you stay well informed of the latest developments in complementary medicine and allow you to provide your patients with a more in-depth, holistic understanding of how their dietary habits can affect their eye health.
Foods to avoid if you have glaucoma
Coffee
Coffee has been shown to increase intraocular pressure (IOP) and cause it to remain elevated for at least 90 minutes.1 The Blue Mountain Eye Study found a link between patients with primary open-angle glaucoma (POAG) who reported regular caffeine consumption and a higher mean IOP.2
Pasquale et al. also noted a positive correlation between developing pseudoexfoliative glaucoma and caffeine consumption.3 A possible explanation for this is that the plasma and aqueous levels of homocysteine can potentially be elevated by coffee which is associated with the development of pseudoexfoliation glaucoma and open-angle glaucoma.4
A recent multicenter study found that patients who consumed high levels of caffeine (>480mg or ~four cups of coffee a day) and already had a higher genetic predisposition for high IOP had a 0.35mmHg higher IOP than those who consumed less than 80mg daily.
For patients who consumed three cups daily (>321mg daily) and had the highest genetic predisposition for high IOP, there was actually a 3.9-fold higher glaucoma prevalence compared to those who consumed minimal or no caffeine and had low genetic risk scores.3
Bae et al. performed a study through the Korea National Health and Nutrition Examination Survey and found that coffee consumption is associated with OAG, whereas no significant association was found between the consumption of tea or soft drinks and OAG.4
The participants of the study who drank coffee had an increased risk of already having OAG (odds ratio [OR] 2.4, p = 0.011).4 When this analysis was stratified based on sex, there was a greater association between coffee consumption and OAG in men but not women.4
A good, general recommendation for patients would be one cup of coffee a day, as this would be unlikely to affect their glaucoma. However, if they are drinking high amounts of coffee, they should consider decaffeinated. This is particularly important for patients who already have a family history of glaucoma.
Water
Hydration is always important for good health, but excessive amounts of water in short periods of time can be dangerous. Drinking a quart of water in less than 5 minutes has been shown to increase intraocular pressure; instead, advise your patients to drink small amounts of water often to stay hydrated.6
The mechanism behind the increase in IOP was studied by Brucculeri et al. They studied 16 young and healthy individuals during dehydration and 1 hour after rehydration (14mL H2O/kg body weight).7 They measured hematocrit, total plasma osmolality, plasma colloid osmotic pressure, along with IOP.7
In the second series of this study, rehydration was performed after pre-treating the individuals with a placebo or topical carbonic anhydrase inhibitor, specifically 2% dorzolamide.7 In both series of the study, the mean IOP increased significantly 15 minutes after water ingestion and remained elevated compared to baseline for 45 minutes.7
This being the case, it has been concluded that the increase in ocular pressure is independent of active bicarbonate pumping, and thus, factors affecting aqueous drainage must explain the observable increase in IOP.7
Alcohol
Alcohol has been shown to decrease IOP within a short period of time (60 minutes).8 Additionally, a study performed in Korea noted a significant association between alcohol consumption and increased IOP.9 It is important to consider that this study was conducted through a survey of the population.
Through the study, it was found that alcohol consumption more than 2x per week is associated with increased IOP in men without OAG.9 In women with OAG, drinking alcohol more than four times per week was associated with an increase in IOP.9
The study raised the idea that patients who are in need of controlling their IOP should consider the effects of alcohol consumption and further reduce alcohol intake if possible. A meta-analysis performed by Stuart et al. also suggested that there is a positive association of 1.18 with a 95% confidence interval (CI) of 1.02 to 1.36 between alcohol and OAG.10
Substances with no effect or little effect on glaucoma
AREDS supplements
Age-Related Eye Disease Studies (AREDS) supplements were shown to have no effect on the diagnosis or progression of glaucoma in a prospective study by Garcia-Medina et al.11 In a sample of patients with mild to moderate POAG, there was no measurable difference between groups that took the antioxidant supplements versus those that did not.
The components of AREDS include vitamins C and E, beta-carotene, copper, lutein and zeaxanthin, and zinc.12 These ingredients were individually studied by Sethi et al., and it was found that there is no association between the ingredients and a lower risk of glaucoma.12 The Age-Related Eye Disease Studies demonstrated that the use of AREDS is important in slowing the progression of macular degeneration.
Omega-3 and omega-6 supplements
One of the proposed contributors to the pathogenesis of glaucoma is an imbalance between omega-3 and omega-6 fatty acids.13 While a recent prospective study has shown a higher risk for glaucoma linked to a high omega 3:6 dietary ratio intake (lower omega-6 amounts),9 the addition of omega-3 supplements did not yield any benefit to POAG patients in the Garcia-Medina study.13
However, in another study done by Downie et al., oral omega-3 supplementation for 3 months significantly reduced IOP in normotensive adults.14 Additionally, Ye et al. proposed the mechanism that glaucoma patients have lower omega-3 fatty acid blood levels, especially docosahexaenoic acid and eicosapentaenoic acid.15 Dietary omega-3 supplementation could potentially normalize these levels, but this idea is yet to be proven.
Given the contradictory evidence from the studies as well as the additional systemic health benefits from both omega-3 and omega-6, it currently would not be recommended to advise patients to change course on their fatty acid intake. It is important to keep in mind that there may be a therapeutic potential of omega-3 supplementation for reducing IOP.
Vitamins
Vitamins B and E, as supplements, have not been shown to have any effect on IOP.16 Vitamin C can have a lowering effect on IOP; however, massive doses are needed to cause such an effect, which also leads to detrimental side effects such as diarrhea and dehydration.17
Vitamin E has an antioxidant effect that improves retinal ganglion cell survival and decreases changes in trabecular meshwork cells. However, there has been no demonstrated association between its consumption and the risk of POAG.12
A new meta-analysis regarding vitamin A was recently conducted, which included 141,988 people, 1,776 of whom had glaucoma.18 The analysis showed that vitamin A has a protective effect against glaucoma, with an odds ratio of 0.63.18 However, it is important to consider that a high-dose intake was required to achieve these effects.
Marijuana
Much has been said about the link between marijuana and glaucoma, but research continues to confirm that current medical therapies are much more effective at treating glaucoma.19 Marijuana has been shown to decrease IOP by 25% for a short period of time,20 however, for this to be effective, it would need to be taken up to 8 times a day.
The decrease in IOP occurs whether the cannabinoids are administered orally, intravenously, or by inhalation.21 Oddly enough, there is no decrease in IOP if it is applied topically to the eye.21
Given the side effects of increased risk for emphysema and lung cancer, in addition to loss of concentration and coordination, it would be best to advise patients against using marijuana for the purpose of lowering IOP. Long-term studies have also shown no proven effect on glaucoma.22
Recommended foods and drink for glaucoma patients
Nitrate-rich leafy greens
In two large studies, eating a diet rich in nitrates, typically in the form of leafy green vegetables, has been associated with a 20 to 30% lower risk of POAG. In patients with early visual field loss close to central vision, the association was greater, showing a 40 to 50% lower risk.23
Dietary nitrates increase nitric oxide (NO), an area of recent increased interest for POAG therapeutics. In POAG, the endogenous NO pathway is suspected to be compromised, and a diet rich in leafy greens, such as spinach, kale, Swiss chard, lettuce, and arugula, may offer an alternative pathway to increase NO production.
Fruits and vegetables
While vitamin supplements have not been shown to have an effect on glaucoma, multiple large studies have supported the relationship between eating foods high in antioxidants, including vitamin A, vitamin C, and carotenoids, and a decreased glaucoma risk.24
Greater than one serving a week of collard greens or kale decreased the odds of glaucoma by 57%, while consuming more than two servings a week of oranges or peaches also decreased the odds of glaucoma. Higher consumption of carrots and spinach also showed some association with protective trends. Giaconi et al. conducted a study that confirmed a decreased likelihood of glaucoma in African American women who consume fruits and vegetables high in the above antioxidants.24
Given the associated correlation between glaucoma and systemic diseases, such as diabetes and heart disease, it makes sense that a heart-healthy diet of fruits and vegetables may help decrease the risk of glaucoma. Additionally, Li et al. have shown that diabetes plays a significant role in poorer outcomes after glaucoma management surgery.2
A good mantra to remember:
“If it’s good for your heart, it’s good for glaucoma. If it’s good for your brain, it’s good for glaucoma.”24
Tea
The flavonoids in tea are known to reduce oxidative stress and improve blood flow, which are both mechanisms suspected to play a role in glaucoma development and progression. A study by Wu et al. showed that patients who consumed one cup of hot tea daily had a 74% reduced risk of glaucoma compared to those who drank none.26 The study did not differentiate between the type of tea consumed (i.e., green, black, or white).
A further study went on to show that green tea in particular was useful for decreasing IOP and reducing the risk of glaucoma.27 In this study, there was a reduction of anywhere from 2 to 5mmHg in IOP in the participants who consumed green tea versus a placebo.27
Ginkgo biloba
Ginkgo biloba has been found to affect several different pathways of importance to glaucoma, including increasing ocular blood flow, improving retinal ganglion cell survival, and protecting against oxidative stress.
Multiple studies have shown improved visual function and decreased progression of visual field loss in patients with glaucoma.28 However, a recent study in China found ginkgo biloba had no effects on patients with normal-tension glaucoma.29
Saffron
A pilot study done in Iran (a leading producer of saffron) showed that daily intake of aqueous saffron extract for 3 weeks reduced IOP in patients with glaucoma. The proposed mechanism was the antioxidative effects of saffron.30
Moderate exercise
A conversation with patients about dietary recommendations typically goes hand-in-hand with recommendations for a non-sedentary lifestyle. One study revealed that aerobic exercise (such as walking, swimming, and biking) at a brisk pace for 30 to 45 minutes three to four times a week lowered IOP and improved blood flow to the eye and brain.31
One of the proposed mechanisms for this is that exercise increases the pressure in the eye, which further leads to an acceleration of aqueous outflow during exercise.32 However, there are certain exercises that can increase eye pressure, such as yoga poses that incorporate inversion.33 This includes poses like downward-facing dog pose, handstands, and additional exercises in which a person may hold their breath while straining.33
Another study showed that all measures of physical activity—average steps per day, minutes of non-sedentary movement, and greater time doing moderate-to-vigorous physical activity—were associated with slower rates of visual field loss in patients being treated for glaucoma.34 A meta-analysis revealed that exercise in sedentary people had a greater effect on lowering IOP than in those who were already active.35
Stress that exercise has an even greater effect on lowering eye pressure in your patients who are not active than in those who are currently active.36
What to tell your glaucoma patient
Based on the current research, there are several recommendations that can be made for your glaucoma patients beyond conventional medical therapies.
In addition to counseling your patients on the importance of good compliance with topical therapies and follow-up visits, consider inquiring about their daily caffeine intake, diet, and physical activity level. The science supports limiting coffee, eating your fruits and vegetables (particularly those leafy greens), and a routine of moderate physical activity.
Glaucoma patients should be advised to:
- Limit coffee to one cup and supplement with hot tea, which has been shown to have beneficial properties.
- Add nitrate-rich leafy greens to their diet, including kale, Swiss chard, spinach, collard greens, arugula, and lettuce.
- Consume more fruits and vegetables rich in vitamins A, C, and carotenoids (i.e., oranges, peaches, carrots).
- Avoid excessive amounts of water in short periods of time.
- Include moderate exercise, such as walking, swimming, biking, at least 30 minutes three to four times a week.
Conclusion
To continue being a gatekeeper for your patient’s health and playing a role in their health education, provide them with the information and tools to navigate their glaucoma diagnosis with confidence, knowing they are doing everything they can to decrease their risk for further progression and vision loss.
