Industry-funded scientific argument of the week: do blueberries prevent dementia?

I have posted several studies funded by blueberry trade associations over the years, including my all-time favorite, the one about prevention of erectile dysfunction.  Yes!

Can we please use some common sense here?  I love blueberries, grow and harvest them on my Manhattan terrace, and eat them whenever I can—but not because I think there is the remotest chance that they alone will keep me from dementia.

But scientists are seriously debating whether blueberries do or do not improve cognitive function in the elderly.

Study #1: Hein S, Whyte AR, Wood E, Rodriguez-Mateos A, Williams CM. Systematic review of the effects of blueberry on cognitive performance as we age. Journal of Gerontology: Series A. 2019;74(7):984-95

Conclusion: “Findings from these studies indicate that cognitive benefits may be found for delayed memory and executive function in children and for delayed memory, executive function, and psychomotor function in older healthy and MCI [mild cognitive impairment] adults”.

Funder: “This work was supported by an unrestricted grant from the Wild Blueberry Association of North America.”

The Debate:

• Errors or irreproducibility in effect size calculations and incomplete reporting of results in “Systematic Review of the Effects of Blueberry on Cognitive Performance as We Age:  The combination of irreproducible effect size calculations, selective reporting of effects, and general errors in systematic review methodology result in a misrepresentation of the strength of evidence about blueberries and cognitive performance.

Study #2:  The effect of blueberry interventions on cognitive performance and mood: A systematic review of randomized controlled trials.

Conclusion: “Based on the current evidence, blueberries may improve some measures of cognitive performance.”

Funding: The article, still in press, states that the authors declare no competing interests but provides no information about study funding.

The debate: 

• There is No Meta-Analytic Evidence of Blueberries Improving Cognitive Performance or Mood:  Based on the current research, however, researchers should avoid drawing any definitive conclusions regarding the effects of blueberries on cognitive performance.
• In Response to “There is No Meta-Analytic Evidence of Blueberries Improving Cognitive Performance or Mood”:  The authors of study #2 say that they “echo the conclusions of the authors [of the critique] that state that while both our review and their analysis provide limited support for the use of blueberry interventions, this should not be interpreted as conclusive evidence for a lack of efficacy but rather that further trials are required to resolve existing limitations.”

My Comment: Of course blueberries are healthy and wouldn’t it be wonderful if all you had to do to prevent dementia was to eat some every day.  Skeptic that I am, I am happy to see widespread agreement that these studies do not constitute conclusive evidence.  Of course eating blueberries (or any other fruit) is healthy; eating fruits and vegetables is healthy.   This kind of research is about getting you to eat more blueberries, rather than any other kind of berry or fruit.