Flavonoids and cognitive function: a review of human randomized controlled trial studies and recommendations for future studies

Abstract

Evidence in support of the neuroprotective effects of flavonoids has increased significantly in recent years, although to date much of this evidence has emerged from animal rather than human studies. Nonetheless, with a view to making recommendations for future good practice, we review 15 existing human dietary intervention studies that have examined the effects of particular types of flavonoid on cognitive performance. The studies employed a total of 55 different cognitive tests covering a broad range of cognitive domains. Most studies incorporated at least one measure of executive function/working memory, with nine reporting significant improvements in performance as a function of flavonoid supplementation compared to a control group. However, some domains were overlooked completely (e.g. implicit memory, prospective memory), and for the most part there was little consistency in terms of the particular cognitive tests used making across study comparisons difficult. Furthermore, there was some confusion concerning what aspects of cognitive function particular tests were actually measuring. Overall, while initial results are encouraging, future studies need to pay careful attention when selecting cognitive measures, especially in terms of ensuring that tasks are actually sensitive enough to detect treatment effects.

Anthocyanin-rich plum juice reduces ambulatory blood pressure but not acute cognitive function in younger and older adults: a pilot crossover dose-timing study

“…Five short cognitive interviewer-administered tests [38,39] were administered by trained investigators at baseline and 6h on both testing occasions to determine any acute changes in cognition.…”

“…Although previous studies have found no significant acute effect of anthocyanins from fruit source on cognitive processes, the QGP juice used in the present study had a significant higher content of anthocyanins and therefore there was a possibility that it might induce cognitive effects. In addition, two different cognitive tests that have been shown to be sensitive and target different domains were utilized; Stroop and the Reaction time task [39,56]. Extensive research has been carried out on the long term effect of flavonoid supplementation on cognition [39] with less attention on their acute effects.…”

“…In addition, two different cognitive tests that have been shown to be sensitive and target different domains were utilized; Stroop and the Reaction time task [39,56]. Extensive research has been carried out on the long term effect of flavonoid supplementation on cognition [39] with less attention on their acute effects. Recently, there has been an increase in the body of evidence on the acute effects of flavonoids on cognitive processes such as attention, working memory and psychomotor speed in a general population [57].…”

Enhanced task-related brain activation and resting perfusion in healthy older adults after chronic blueberry supplementation

“…In a meta-analysis, flavonoid supplementation relative to a placebo control group improved cognitive performance in 9 of 15 randomised controlled trials (Macready et al 2009). Subsequent studies found that 12 weeks of wild blueberry juice supplementation (ϳ7 mg anthocyanins per kg −1 ·d −1 ) improved memory function (paired associative learning and word list recall) in adults with mild cognitive impairment (Krikorian et al 2010).…”

Nutrients and brain health: an overview

“…However, it is less obvious how other dietary-derived nutrients or nonnutrient components may impact on the functioning of the brain. Despite this, a large number of dietary intervention studies in humans [1] and animals [3], in particular those using foods and beverages derived from Vitis vinifera (grape), Camellia sinensis (tea), Theobroma cacao (cocoa) and Vaccinium spp (blueberry) have demonstrated beneficial effects on human vascular function and on improving memory and learning [1][2][3]. While such foods and beverages differ greatly in chemical composition, macro-and micronutrient content and caloric load per serving, they have in common that they are amongst the major dietary sources of a group of phytochemicals called flavonoids.…”