This Reuters story reports on an observational study showing a possible association between drinking caffeinated hot tea and lowering the risk of glaucoma.
The story does a good job describing the study design and the lack of treatment options for glaucoma. It also included comments from two independent sources. However, it fell short by not providing enough perspective on how many limitations can occur with this kind of research.
Glaucoma is one of the leading causes of blindness in the world and affects over 55 million people globally. Because vision lost to glaucoma can’t be recovered, much of the research focuses on either slowing progression once it is diagnosed, or preventing the disease by identifying and modifying risk factors. Given that the role of caffeine as a risk factor is controversial, well-conducted research that suggests a protective effect of caffeinated tea is newsworthy, though news stories need to be cautious not to overstate the measured benefits.
Tea is widely available and relatively affordable compared to other prepared drinks.
The story mentions that study participants who drank one cup or more of hot caffeinated tea daily “had 74 percent lower odds of having glaucoma” compared to those who don’t drink hot tea.
Our standard response to a statement like this is to ask, “74% lower than what”? A 74% reduction from an already-small number might not be very meaningful. Absolute numbers would have helped–here’s more about how to provide them and why this is important.
Only potential harm to be considered would be those people who respond to this study by abusing caffeinated tea thinking that more consumption might offer more protection from glaucoma. Excess caffeine can have deleterious health effects. Not including this unlikely scenario in the story seems reasonable.
This was a tough call, as the story does a good job explaining how the research was designed. But it should have been more clear that this was an observational study that can not establish cause and effect. Self-reported dietary information is also notoriously unreliable.
There was no disease mongering.
Two opthalmologists who weren’t involved in the study were interviewed, and we could detect no conflicts of interest.
The story does make brief mention of lifestyle, environmental and diet interventions that may influence glaucoma, but could have made it more clear that none of these have been proven to prevent glaucoma.
Other than water, tea is the most widely consumed beverage in the world.
Although there is existing research investigating the role of caffeine in glaucoma, this study specifically compared the effects of caffeinated and decaffeinated coffee, tea, and soft drinks on glaucoma. The story makes that clear.
The story does not appear to rely solely on the news release. It quotes two independent sources not affiliated with the study.