These Are the Foods to Avoid if You Have Glaucoma

I view myself as one of the gatekeepers for my patient’s health as well as a health educator. When I make a diagnosis of glaucoma or glaucoma suspect, in addition to learning about the medical management of that ocular disease, my 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 of complementary medicine and allow you to provide your patient a more in-depth, holistic understanding of how their dietary habits can affect their eye health.

Foods to avoid to 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 recent multicenter study found that patients who consumed high levels of caffeine (>480 mg or ~four cups of coffee a day) and already had a higher genetic predisposition for high IOP had a 0.35 mmHg higher IOP than those who consumed less than 80 mg daily. For patients who consumed three cups daily (>321 mg 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.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 five minutes has been shown to increase intraocular pressure; instead, advise your patients to drink small amounts of water often to stay hydrated.⁵

Substances with no effect or little effect on glaucoma

Alcohol

Alcohol has been shown to decrease IOP within a short period of time (60 minutes)⁶, but does not have any effect on glaucoma diagnosis or progression. Patients can safely drink alcohol without fear that it may affect their glaucoma. However, as with everything, moderation is advised given the other health ramifications of drinking alcohol.

AREDS supplements

AREDS supplements were shown to have no effect on the diagnosis or progression of glaucoma in a prospective study by Garcia-Medina et al.⁷ 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.

Omega 3/6 supplements

One of the proposed contributors to the pathogenesis of glaucoma is an imbalance between omega-3 and omega-6 fatty acids.⁸ While a recent prospective study has shown a higher risk for glaucoma linked to a high omega 3:6 dietary ratio intake⁹(lower omega-6 amounts), the addition of omega-3 supplements did not yield any benefit to POAG patients in the Garcia-Medina study.⁷ Given the lack of confirmatory 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.

Vitamins

Vitamin A, B, and E, as supplements, have not been shown to have any effect on IOP.¹⁰ 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.¹¹

Marijuana

Much has been made about the link between marijuana and glaucoma, but research continues to confirm that current medical therapies are much more effective at treating glaucoma.¹¹ Marijuana has been shown to decrease IOP by 25% for a short period of time;¹² however, for this to be effective, it would need to be taken many times a day.

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.¹³

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 20-30% lower risk of primary open-angle glaucoma. In patients with early visual field loss close to central vision, the association was greater, showing a 40 to 50% lower risk.¹⁴

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, 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.¹⁵ 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 odds of glaucoma. Higher consumption of carrots and spinach also showed some association to protective trends.

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. 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.”¹⁶

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.¹⁷ The study did not differentiate between the type of tea consumed (i.e., green, black or white).

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.¹⁸ However, a recent study in China found ginkgo biloba had no effects on patients with normal-tension glaucoma.¹⁹

Saffron

A pilot study done in Iran (a leading producer of saffron) showed that daily intake of aqueous saffron extract for three weeks reduced IOP in patients with glaucoma. The proposed mechanism was the antioxidative effects of saffron.²⁰

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, biking) at a brisk pace for 30-45 minutes three to four times a week lowered IOP and improved blood flow to the eye and brain.²¹

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.²²

A meta-analysis revealed that exercise in sedentary people had a greater effect on lowering IOP than in those who were already active.²³ 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.

What to tell your patient

Based on the current research, there are several recommendations that can be made for your glaucoma patients beyond the 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.

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, lettuce.
Consume more fruits and vegetables rich in Vitamin 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.

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.

References

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