Earlier this year, researchers from the University of Cincinnati Academic Health Center reported that 12 weeks of consuming a daily drink of about 500 mL of blueberry juice was associated with improved learning and word list recall, as well as a suggestion of reduced depressive symptoms (Journal of Agricultural and Food Chemistry, 2010, Vol. 58, pp 3996–4000).

The study was said to be the first human trial to assess the potential benefits of blueberries on brain function in older adults with increased risk for dementia and Alzheimer’s.

The new study, led by Houston’s David Malin PhD, examined the effects of one or two months of consuming a blueberry-enriched diet in aging Fischer-344 rats.

Results showed that animals receiving the blueberry diet performed better than animals not receiving a berry-enriched diet, and that two months of supplementation resulted in a maintenance of the improved performance after the supplementation period ended. No such effects were observed in the one month group, said the researchers.

“One possible explanation [for this observation] is a ‘threshold hypothesis’,” said the researchers. “This hypothesis assumes there is a threshold concentration of antioxidants, particularly longer-lasting fat-soluble antioxidants, needed to maintain alleviation of memory impairment.

“The 2-month diet might have produced a larger surplus of antioxidant nutrients over the threshold, whereas the 1-month diet might have produced only a scant surplus above the threshold. Then, as the antioxidant nutrients are metabolized, the 1-month diet might soon lose its ability to prevent memory impairment, whereas this loss of effectiveness might hypothetically take much longer after the 2-month diet,” they added.

Furthermore, rats on the blueberry diet increased their memory scores, while the control animals displayed a decline in memory scores.

“The present study is encouraging in terms of potential human application,” wrote Dr Malin and his co-workers. “First, the present results suggest that even a relatively brief blueberry diet might produce measurable benefits. Second, the benefits of several months of the diet might be maintained for a considerable period after the diet is interrupted. Third, blueberry supplementation might possibly reverse some degree of memory impairment that has already developed.

“This raises the possibility that this sort of nutritional intervention might still be beneficial even after certain memory deficiencies have become evident,” they added.