The Effect of Coffee and Diet on Intraocular Pressure (IOP)
Intraocular pressure (IOP) is a key modifiable risk factor in the development and progression of glaucoma, a leading cause of irreversible blindness worldwide. While IOP can be influenced by several factors, including genetics, age, and ocular anatomy, lifestyle and diet—especially caffeine consumption—are also important considerations. Coffee, being the most widely consumed caffeinated beverage globally, has drawn attention for its potential effects on IOP.
Caffeine, the main active ingredient in coffee, is known to transiently increase IOP. Several studies support this link. A well-cited study published in Investigative Ophthalmology & Visual Science (1997) found that a 200 mg dose of caffeine (approximately one to two cups of coffee) resulted in a significant IOP increase of around 1–4 mmHg in both normal subjects and those with glaucoma. This effect was most notable 30 to 90 minutes after ingestion and typically returned to baseline within a few hours.
Further evidence comes from the Blue Mountains Eye Study, a large population-based study in Australia. It reported that individuals who consumed more than 500 mg of caffeine per day (about five cups of coffee) had higher mean IOP and a slightly increased risk of developing glaucoma, especially if they already had a family history of the disease. However, the effect size was modest, and causality could not be definitively established.
Not all studies agree on the magnitude of this effect. A 2012 study in Investigative Ophthalmology & Visual Science found that regular coffee drinkers exhibited some degree of tolerance, suggesting the acute IOP-raising effect of caffeine may diminish over time. Thus, occasional or new coffee drinkers may be more sensitive than habitual consumers.
Beyond coffee, other dietary factors can influence IOP. Alcohol has been shown in some studies to temporarily lower IOP, though this is not considered a viable or healthy management strategy. On the other hand, diets high in trans fats and saturated fats may negatively affect ocular health by contributing to systemic inflammation and vascular dysfunction, which could indirectly influence IOP.
Conversely, diets rich in antioxidants and omega-3 fatty acids—found in foods like leafy greens, oily fish, and nuts—may have protective effects on the optic nerve and support healthy IOP regulation. For example, high intake of nitrate-rich vegetables (like spinach and beets) has been associated with a reduced risk of glaucoma, possibly due to enhanced blood flow and nitric oxide-mediated relaxation of ocular tissues.
Hydration also plays a role. Drinking a large volume of water in a short time can temporarily increase IOP, particularly in glaucoma patients. This “water drinking test” is sometimes used in clinical settings to assess outflow facility in the eye.
In conclusion, while moderate coffee consumption appears safe for most individuals, those with glaucoma or a high risk of developing it should be mindful of caffeine intake. Dietary patterns emphasizing whole foods, antioxidants, and omega-3s may support overall ocular health and help maintain stable IOP levels. Regular eye exams and consultation with an ophthalmologist remain essential for anyone concerned about glaucoma risk.