Daily blueberry consumption demonstrably improves word retrieval, memory and cerebral blood flow in older adults with mild complaints or risk factors. In people with already-established dementia the effect appears minimal, and mechanistic evidence in humans remains limited.
Blueberries and related red/blue fruits contain anthocyanins and other polyphenols, compounds that have been linked to better cognitive function in older age in several clinical studies. A randomised controlled trial in 50-65-year-olds with insulin resistance and memory complaints showed that daily blueberry supplementation significantly improved word retrieval (p=0.003) and strengthened the ability to resist memory interference (p=0.04). Participants also reported less difficulty with memory storage in daily life. The same study additionally found that elevated blood insulin levels normalised, suggesting that metabolism plays a role in the protective mechanism.
A systematic review of 11 randomised controlled trials concludes that berry products (frozen blueberries, concentrate, drinks, capsules or extract) have beneficial effects on multiple cognitive domains in older adults, including memory, attention, processing speed, executive function and resting cerebral blood flow. This review focused on people without cognitive impairment or with mild complaints, not on people with already-established dementia.
Human studies with blueberry or Concord grape juice supplementation in people with mild cognitive impairment also showed improved verbal memory scores. Two other clinical studies reported small improvements in spatial memory and brain activity in people with mild cognitive complaints following polyphenol supplementation. The effects in these studies are limited in magnitude and the total number of studies is still small.
Animal models and laboratory studies provide indications that polyphenols from blueberries and strawberries reduce oxidative stress and inflammation in the brain, improve signal transmission between nerve cells and may stimulate the formation of new brain cells in the hippocampus (the memory centre). Whether these mechanisms directly protect against Alzheimer's or Parkinson's disease in humans has not yet been sufficiently demonstrated; the evidence for that link is so far confined to animal models.
There are also some caveats. In people with already-established dementia, blueberries and other polyphenols appear to have little or no effect; the potential benefit therefore seems most relevant as prevention or at an early stage of complaints. It is also notable that the simultaneous intake of blueberries and fish oil in one study showed no cognitive improvement, whereas each did so individually. This is an unexpected finding that requires further research. Finally, a large three-year randomised trial (604 participants) examining the MIND diet, of which blueberries are an explicit component, is currently underway, but its results are not yet available.
The claims are based on one randomised controlled trial (PMID 35458181), one systematic review of 11 RCTs (PMID 35217779), several smaller clinical studies (PMID 19640963, 33099465), a design article for a large RCT (PMID 33434704), and review articles drawing primarily on animal and laboratory data (PMID 29141966, 18211020, 11976192). Total participant numbers across the human studies have not been tallied exactly but are estimated at approximately 600-900 persons.