Here’s what we thought could have been handled better:
The story included some important caveats, and sought out an independent perspective to provide nuance to the reporting. But these strong points were overshadowed by the larger failure to grasp the quality of the evidence.
Parkinson’s is a progressive disease which causes tremors and other movement symptoms that typically worsen over time. Patients often have considerable difficulty carrying out everyday tasks, and some become severely disabled. While there are effective treatments, we currently don’t know if there are modifiable factors that can prevent Parkinson’s disease from developing in the first place. These results are interesting because they suggest that certain dietary habits may be associated with lower risk. It will take much more careful research to prove whether these habits are, in fact, protective.
The cost of berries and other foods rich in antioxidants is not in question.
It should be possible to calculate absolute risks from the data in this cohort study. However, this story reported only relative risks, which likely overstate the magnitude of the potential benefit.The absolute risk reduction for dietary changes and Parkinson’s risk is likely to be very small.
The story spends most of its time discussing the potential health benefits of berries. We’re not aware of any harm attributable to berry consumption (provided they are the edible kind).
And the story included this quote from the author:
“There are no harmful effects from berry consumption, and they lower the risk of hypertension too,” Gao added.
The story used cause-and-effect language to describe the findings of this observational study, which as we’ve noted repeatedly is inappropriate. We reiterate our call for journalists to read our primer on observational studies and stop using this kind of language.
We were pleased to see that the story mentioned some limitations of the study, and called for more research. But we think it missed one of the more important caveats: the fact that people who eat a lot of berries and drink green tea and red wine may differ in important ways from those who don’t eat and drink these things. It’s very difficult for a study such as this to account for all of those differences.
The story quoted an independent expert, who cautioned that people who already have Parkinson’s disease won’t benefit from eating berries or other flavonoid-rich foods.
There aren’t really any effective alternatives for preventing Parkinson’s disease, so we’ll rule this not applicable.
The availability of these foods is not in question.
While this may be the first study to document a relationship specifically between berries and Parkinson’s, there have been studies documenting possible benefits from similar dietary approaches that involve antioxidant-rich foods, such as the Mediterranean diet. The story could have mentioned this research.
We don’t think this story was based on a press release.