The effects of anthocyanins on cognition and cardiometabolic markers

Anthocyanins are polyphenols, a class of bioactive compounds which research suggests may help maintain or improve cardiovascular health and cognitive function. This PhD thesis examines two sources of anthocyanins, blueberries and hibiscus, and explores their possible effects on vascular health, glycaemic control and cognitive function. A systematic review of 20 studies showed that anthocyanins did have positive effects on cognitive performance and that tests of verbal memory and executive function were sensitive to anthocyanin intervention. These findings informed the selection of cognitive tests for use in the experimental studies presented in this thesis.
A further systematic review identified 18 studies which met the inclusion criteria focussing on blueberries and examined their impact on markers of glycaemic control. This review concluded that blueberry intake significantly reduced postprandial glucose and insulin peaks with less evidence for effects on other glycaemic markers. The effects of wild blueberry powder on measures of cognitive performance, cardiovascular markers (blood pressure, glucose and insulin) and satiety were investigated in a four-arm dose-response crossover study in 24 healthy participants No significant effects of blueberries were observed for blood pressure or for the domains of verbal memory, attention or executive function. Dose-dependent effects on postprandial glucose and insulin, including attenuation of glucose and insulin peaks were observed. In addition, dose dependent increases in satiety markers were found.
Hibiscus Sabdariffa is a less well-studied source of anthocyanin. The cardiovascular and cognitive effects of hibiscus were explored in a systematic review of 17 trials. No studies of hibiscus on cognitive function in humans were identified. Hibiscus significantly lowered systolic blood pressure, particularly in individuals with elevated baseline levels, and reduced LDL cholesterol. Hibiscus treatment effects were indistinguishable from blood pressure lowering pharmaceuticals. These findings suggest that hibiscus could reduce cardiovascular risk. A pilot study was designed to explore the acute effects of hibiscus on metabolic and cognitive functions in 20 overweight individuals. Hibiscus consumption significantly reduced postprandial glucose and improved aspects of memory and executive function, though no effects on blood pressure were observed. These preliminary findings suggest that further investigation of the effects of hibiscus consumption on cardiometabolic and cognitive endpoints are warranted.
Taken together the systematic reviews, meta-analyses and experimental studies presented in this thesis highlight the potential for blueberries and hibiscus to positively impact cognitive function, vascular health, and glycaemic control.