The Acute Effects of Low and High doses of Blueberry Flavonoids on Vision, Cognition, and Mood

Blueberries3rd Year project: Lynne Bell & Charlotte Martin

Supervised by Dr. David Field & Dr. Claire Williams, March 2012

 

The importance of eating a diet rich in fruit and vegetables has been highlighted in recent years. Concerns over health issues such as obesity and the increasing costs of public funded healthcare have prompted research into the benefits of healthy eating. Much of this research has focussed on the cardiovascular system; however, increasing numbers of studies show beneficial effects to the brain. Flavonoids are micronutrients found in food groups such as berries and chocolate. Blueberry flavonoids have been linked to improvements in cognition such as memory enhancement and increased speed of processing. Cocoa flavanol, found in dark chocolate, has been linked to improvements in mood and aspects of visual perception such as improved night vision.

This third year project investigated whether blueberry flavonoids would have the same effects on night vision and mood as previously shown for cocoa flavanol. We recruited 25 fellow undergraduate students to take part in the study. Each participant had to attend three separate sessions where they were asked to consume a drink made from blueberry powder mixed with orange squash. They then completed a series of tests after a time delay of approximately two hours. On each occasion the drink contained a different dose of blueberry; a control drink contained no blueberry and the other two drinks contained high and low doses respectively. Neither the participants nor the experimenters knew which drink was given at each session to prevent any bias in test performance. Optical lenses and prisms were used to measure the participants focussing ability (accommodation) and binocular vision (convergence). Night vision was measured using a contrast sensitivity test. The participants had to sit in the dark and read letters on a screen that became progressively similar in luminance to the background. Cognition was measured using a speed of processing task where the participant had to rapidly transpose a list of numbers into corresponding symbols according to a key. Mood was measured using rating scales for adjectives such as ‘happy’.

Flipper

Optical lens flippers similar to those used for accommodation and convergence testing  

Contrast sensitivity test

An example of a contrast sensitivity test  

 Cognitive test

An example of a cognitive test

 

The results for each test showed that consuming blueberries caused a slight improvement, i.e. performance was better for blueberry conditions compared to the control condition, and high doses of blueberry gave a stronger effect than low doses. However, these improvements were not statistically significant, except in the case of convergence (binocular vision) testing. The failure to produce statistically significant cognitive, mood, and visual effects was attributed to problems with the method. In particular, the time between consuming the drink and completing the tests varied slightly between participants. The release of flavonoids into the blood stream after consumption follows a time-related curve, so testing at the same time is critical. The significant convergence (binocular vision) finding is due to be published shortly. A proposed explanation for this effect is an increase in blood flow to the eye muscles. Anthocyanins, the main flavonoids in blueberries, have vasoactive properties; they cause blood capillaries to dilate leading to improved blood circulation.

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