We love to draw connections wherever possible — especially when it’s relevant to everyday life. So, when we (the royal “we” in this case) get the chance to write about coffee, there’s a bit of a rush associated. That’s not the caffeine talking in this case. Rather, it’s just the thrill of diving into such a relevant topic. Caffeine may well be the world’s favorite drug, and it’s certainly popular with us writers at CAKE magazine.
We know that caffeine can cause a short, sharp increase in blood pressure, even in those with normally low blood pressure. Many are familiar with the jolt from a shot of good espresso, and enjoy the experience.
But we’re here today to dig through the relationship between a different type of pressure: intraocular pressure (IOP). How does caffeine consumption affect IOP? Does it have an effect on glaucoma?
IOP and Coffee: Collecting Data
Establishing a causal link between such multifactorial conditions like IOP and glaucoma with caffeine is no easy task. However, the enormous amounts of data gathered from the UK Biobank have made the job a bit easier. There’s always a difference between quality and quantity of data. However, as Napoleon Bonaparte said, “Quantity has a quality all its own.”
In this case, the quantity of participants was a whopping 121,374 people, representing an age range of 39-73 years. These were both coffee and tea drinkers (it’s the UK, after all), with data collected between 2006-2010 and IOP measurements taken in 2009. Another subset of 77,906 participants reported caffeine intake during food questionnaires between 2009-2012.
In addition to IOP measurements, the study examined the relationship between caffeine and glaucoma, with 9,286 cases and a control group of more than 189,000 participants.
So, just in case the picture isn’t clear, there were a lot of people involved in this study. This is the kind of work we’ve come to expect from the UK Biobank, and we’re thoroughly grateful.
IOP and Coffee: So, What’s the Link?
Perhaps surprisingly, higher levels of caffeine consumption (north of 232 mg/day) was associated with a 0.10 mmHg lower IOP than those who consumed less than 87 mg/day. For reference, an average cup of brewed coffee can contain anywhere between 70-140 mg of caffeine — but to make your life easy, just imagine it’s about 100. Tea usually contains half as much, but that of course depends on the type of tea, method and length of steeping, and so on.
So, moderate caffeine consumption can moderately lower IOP. A very high level of caffeine consumption, however — nearing 500 mg per day — was associated with an increase in IOP of 0.35 mmHg.
These are pretty mild links, so no significant conclusions can be drawn from them. As reason would suggest, a moderate amount of caffeine consumption isn’t bad for you and in some cases can be good for you. Hooray, right?
Genetic Risk Factors: Coffee and Glaucoma
There is one significant takeaway from the study that deserves attention. It’s this: Among those with the highest genetic predisposition for glaucoma, a high caffeine consumption (more than 321 mg/day) showed prevalence of glaucoma 3.9 times higher than those with the same risk factors who consumed no caffeine.
While that might not mean it’s time to sound alarm bells, it should at least raise a red flag. Those who are aware they have genetic risk factors should probably be careful about their caffeine consumption. That’s what the study suggests, at least.
So, what does this mean for coffee lovers and for their doctors? For those who consume a reasonable amount of coffee and know they don’t have significant genetic risk factors for glaucoma, everything seems to be hunky dory. Carry on with your morning cup — or afternoon, or whatever suits you. Tea drinkers can feel just as comfortable, of course.
It’s a good idea in general to keep an eye on your caffeine consumption, as the drug finds itself in more and more places these days. It’s especially valuable to keep an eye on it if you know you’re at greater genetic risk of developing glaucoma.
For most of the world, this won’t be an earth-shaking study. But the link between genetic predisposition to glaucoma and caffeine is indeed an interesting one, and may give researchers another thread to pull on in the future. We’re looking forward to seeing where this goes and will keep you up to date.