Coffee plays a big part of our daily lives. With around 2 billion cups drank globally each day, and new coffee trends like Dalgona coffee taking the world by storm, even during lockdown: it’s fair to say life just wouldn’t be the same without it.
Caffeine is a natural (and really delicious) way of getting us to spring into energy mode, as it stimulates our brain and helps us feel awake and alert (just like putting your contact lenses in after your morning shower). In fact, moderate levels of caffeine can be good for your vision in many different ways: from coffee soothing dry eyes to protecting eyes against retinal damage. But as with everything, overdoing it could have negative effects for your eye health, both short and long term.
Caffeine: how much should you drink?
It’s hard to give a definitive answer, as coffee’s caffeine content varies a lot: ranging from 50 to over 400mg per cup. A regular cup you make at home will provide around 95mg of caffeine, while a Starbucks grande Americano packs over 300mg. NHS research, spanning across 200 studies, found that drinking 3 cups of coffee a day could be beneficial for most people. Moderate coffee consumption was linked to lower risks of diabetes, liver disease, dementia and even some types of cancer.
Raw coffee beans contain chlorogenic acid (CGA), an antioxidant that helps to reduce blood pressure and improve circulation. CGA can help to protect the body from a condition called hypoxia, caused by a lack of oxygen. Your retina is particularly vulnerable to hypoxia, so drinking coffee could help prevent any damage to your eyes and vision.
Tests using CGA in its purest form have shown that it can prevent deterioration of the retina, but there is yet to be solid proof that drinking coffee can help with this.
However, consistently going above the recommended amount could impact your health and vision, as it puts you in higher risk of developing chronic conditions such as glaucoma.
Can coffee cause glaucoma?
Caffeinated drinks are known to increase blood pressure, as well as pressure in your eyes. Consistently high levels of eye pressure are known to cause glaucoma, so there could easily be a link between your coffee habit and one of the world’s leading causes of blindness.
A 2012 study by Harvard Medical school found that there was indeed a link between drinking 3+ cups of coffee and developing exfoliation glaucoma. This happens when a build-up of fluid in the eyes turns up the pressure on the optic nerves. They also found that this increase in risk of developing exfoliation glaucoma was more prominent in those with a family history.
While this study could show a link, it doesn’t mean that if you drink lots of coffee you’ll definitely develop glaucoma. For example, many participants of the study had a family history of glaucoma, which has been proven to be a key factor in developing the condition. It’s all about how your body handles caffeine - so it’s far from a one-size-fits-all approach. These results are also based on regular overconsumption: more about consistently having 3+ cups of coffee every day, rather than drinking an extra cup on a busy Monday.
Can coffee help to prevent Type 2 diabetes?
Regular coffee drinkers are also seemingly less at risk of Type 2 diabetes and the complications that can arise from it, including diabetic retinopathy. In 2014, researchers at Harvard tracked a group of participants for over 20 years, monitoring their coffee intake closely. They found that those who increased their daily coffee intake by 1 cup or more over the time had an 11% lower risk of developing Type 2 diabetes. Those who decreased their intake by a cup or more increased their risk by 17%.
This causes a bit of confusion, as those who have already developed Type 2 diabetes are advised to avoid drinking too much coffee. A 2004 study by the ADA showed that a dose of caffeine before eating resulted in higher blood glucose after the meal and an increase in insulin resistance. It could be the case that the positive effects of coffee are down to the ways that your body metabolises caffeine, than coffee itself.
Overall, it still isn’t completely clear how coffee affects eyesight and why it seems to have different effects to other caffeinated drinks such as tea and energy drinks. As with everything, it’s a good idea to enjoy coffee in moderation and try to keep on the lower side of the recommended daily caffeine allowance of 400mg.