Following a very small study of 26 people, scientists at the University of Exeter claimed that drinking about two tablespoons of blueberry juice concentrate improved the brain function of 12 adults, partially based on magnetic resonance imaging (MRI) function tests. The study lasted only 12 weeks.
The news release exaggerates the importance of such a brief limited study, and it doesn’t include any numbers that would help readers understand any changes that were observed. On the plus side, the release does disclose that the study received financial support and samples from a blueberry supplement manufacturer.
The volume of nutrition advice hitting the daily news cycle is overwhelming readers’ capacity to keep up and sort the evidence-based news from the purely promotional. News releases like this tend to straddle both the good and the bad.
While fruits and vegetables are uniformly considered healthful, this claim of brain changes from a few tablespoons of blueberry concentrate is backed by very thin “evidence” from a very preliminary and limited study. We wish the release had explained the limitations of small, short duration studies.
We’ve seen this before and described some of the problems in a blog post on why readers need to be skeptical about nutrition claims relating to brain health — and how you can’t eat your away out of dementia risk.
Moreover, these sorts of releases and news stories further perpetuate the notion that supplements provide remarkable and clinically meaningful health benefits despite the fact that with almost no exceptions, the research has not borne this hope out.
There is no mention of the cost of this blueberry concentrate. According to the manufacturer’s website, a 473ml bottle of BlueberryActive Concentrate sells for £17.99 British pounds, or $21.85 in US dollars. Thirty blueberry capsules cost $13.35 in US dollars.
The release gives us the broadest brush about benefits, but does not provide numbers or quantify how much improvement occurred.
It states that “brain blood flow, brain activation and some aspects of working memory were improved in this group of healthy older adults” and “Compared to the placebo group, those who took the blueberry supplement showed significant increases in brain activity in brain areas related to the tests.”
How much improvement was there? How did brain activity change before and after taking the supplement?
But even with those numbers, brain activity is not a clinically meaningful measure. It’s a surrogate end point, not a measurable clinical benefit.
There was no statement about harms, not even a statement declaring there are none.
The study from the get-go wasn’t sufficiently powered (meaning it didn’t have enough study volunteers) to detect changes in cognitive performance. The published report notes that: “Cognitive function was assessed, as a secondary outcome, although the study was not sufficiently powered to detect changes in cognitive performance.”
How many more people would have been required to provide sufficient power? What limited the researchers from taking the time to recruit them?
The release included the important fact that a commercial enterprise selling blueberry juice concentrate and blueberry capsules provided the samples and some of the funding for the study.
The published paper states the authors declared they had no conflicts of interest.
The release could have included some of the other factors that are known to reduce risk of dementia including exercise, maintaining a healthy weight, and moderating any alcohol use.
We know blueberry juice is widely available but what about the concentrated blueberry juice used in the study?
The study does not make a claim of novelty, and includes this statement about previous research:
“Previous research has shown that risk of dementia is reduced by higher fruit and vegetable intake, and cognitive function is better preserved in healthy older adults with a diet rich in plant-based foods.”
We think the headline is not justified by the evidence presented.
“Blueberry concentrate improves brain function in older people.”
The statement makes it sound as if this single study of 12 people proves a functional improvement that is permanent, and that is not proven by the limited 12-week study. We also question whether the markers that were used — blood flow and brain activity during tests — can be reliably linked to a permanent change in the individual’s cognitive ability.
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