[FALSE] Does an American study prove that people who consume more than one cup of coffee every day have 3.9 time higher risk of developing eye diseases?

Screenshot of the Facebook post.

The Claim and Our Verdict

• The claim: A Facebook post published June 16, 2021, shares an article about a recent study involving American researchers and claims that people who consume more than one cup of coffee a day have 3.9 times higher risk of developing glaucoma.
• Fact-checking:
  • In the Facebook post, the description does not match the text in the picture. The description says, “people who drink more than one cup of coffee a day,” while the text in the picture is “people with a genetic predisposition towards higher eye pressure who drink three cups of coffee a day.”
  • The study, as mentioned in the claim, was published in June 2021 in the journal of Ophthalmology. It finds that people with the highest genetic predisposition towards higher intraocular pressure (IOP, or eye pressure) who consume more than 321 mg of caffeine a day have a 3.9 times higher glaucoma risk (a three-fold higher risk as mentioned in the claim), compared with those with the lowest genetic predisposition who consume no caffeine. Nevertheless, the study does not conclude that people who drink more than one cup of coffee a day have 3.9-fold higher glaucoma prevalence.
  • The paper concludes that there is no direct correlation between caffeine consumption and glaucoma. The effect is significant only among those with the strongest genetic predisposition to higher IOP. It is worth noting that those who have a genetic predisposition to higher IOP have a naturally greater tendency for developing glaucoma than other people.
  • Moreover, a certain amount of caffeine (say, 321 mg) cannot be simply converted to a fixed number of cups of coffee. The amount of caffeine intake can vary according to different coffee species and cup sizes. Apart from coffee, other kinds of food also contain caffeine.
• Our ruling: Therefore, we rate the claim as FALSE.

News Brief

A Facebook post published June 16, 2021 shares an article entitled “[Glaucoma] Those with a genetic predisposition towards higher eye pressure who drink three cups of coffee a day have triple the risk of developing eye diseases.” In the post description, it says, “Many people like to refresh themselves with a cup of coffee at work. Some people may drink more than one cup a day, and if you do, you need to pay attention. Your risk of developing glaucoma is 3.9 times higher than others.”

As of the issuance of this report, the post had been shared 10 times, and had received 1 comment and 56 likes or reactions.

Fact-checking

In the Facebook post, the description does not match the text in the picture. The description says, “Some people may drink more than one cup of coffee a day, and if you do, you need to pay attention. Your risk of developing glaucoma is 3.9 times higher than others.” However, the text in the picture is that “Those with a genetic predisposition towards higher eye pressure who drink three cups of coffee a day have triple the risk of developing eye diseases.” The Facebook post description only mentions “people who drink more than one cup of coffee a day,” but it does not make it clear whether those people have a genetic predisposition to higher eye pressure. This may create a false impression. Moreover, the wording in the description “drink more than one cup of coffee a day” is different from that in the text of the picture “drink three cups of coffees a day.”

The study, discussed in the Facebook post, was published in June 2021 in the journal of Ophthalmology, entitled “Intraocular Pressure, Glaucoma, and Dietary Caffeine Consumption.” It analyzed data and samples from more than 120,000 participants aged between 39 and 73.

The result of the study is that “habitual caffeine consumption was associated weakly with lower IOP, and the association between caffeine consumption and glaucoma was null. However, among participants with the strongest genetic predisposition to elevated IOP, greater caffeine consumption was associated with higher IOP and higher glaucoma prevalence.” “Compared with those in the lowest IOP polygenic risk score (PRS) quartile consuming no caffeine, those in the highest IOP PRS quartile consuming ≥ 321 mg/day show a 3.90-fold higher glaucoma prevalence.” Generally speaking, there is no association between caffeine consumption and glaucoma. Compared with those with the lowest quartile of IOP PRS, those with the lowest quartile of IOP PRS who consume more than 321 mg of caffeine daily show a 3.9-fold higher glaucoma prevalence. Nevertheless, the study does not conclude that a normal person who consumes more than one cup of coffee a day has 3.9 times higher risk of developing eye diseases. In addition, it is worth noting that those with the highest genetic susceptibility to higher IOP have a naturally greater tendency for developing glaucoma than other people.

A news article published June 7, 2021 by the United Kingdom’s Daily Mail reported the study and converted 321 mg of caffeine to three cups of coffee. The Facebook post cited this Daily Mail article and used the same wording of “three cups of coffee.” But in fact, the amount of caffeine intake varies with different coffee types, cup sizes and other factors.

Screenshot of the Daily Mail article.

To better understand the concept of “321 mg of caffeine,” we take the amount of caffeine in Nespresso coffee capsules as an example. According to the Hong Kong Nespresso website, the caffeine found in a coffee capsule varies according to different coffee species. The types of coffee in the Professional line contain between 50 and 100 mg of caffeine per cup. As such, 321 mg of caffeine is roughly equivalent to 3-6 cups of Nespresso coffee. “Three cups of coffee” is not an accurate saying of 321 mg of caffeine. In addition, caffeine does not only come from coffee, but also other food and beverage. The caffeine consumption mentioned in the study is a sum of the caffeine from many sources, such as coffee, tea, chocolate and so on. Therefore, the daily caffeine consumption cannot be simply converted to a certain number of cups of coffee.