Researchers at the University of Otago in Christchurch, New Zealand, have found that supplementing the diet with kiwi fruit can improve psychological wellbeing and lift fatigue. Raising fruit and vegetable intake has previously been associated with similar psychological benefits, so kiwi was chosen as a fruit rich in vitamin C and other important micronutrients.
A total of 36 healthy young men, average age 21, had their diets supplemented with either one half or two whole kiwi fruit per day, for a six week period. Although there were no observable effects in the half per day group, the two per day group experienced less mood disturbance and less depression. On further analysis, it was found that those participants who had a higher level of mood disturbance at the start of the study, gained the most benefit in these areas; they additionally experienced less fatigue and an increase in vigour.
Two kiwi fruit per day was equivalent in this study to about 212mg vitamin C per day, and the researchers suggest this may be the optimal intake rather than the 60-80mg which is the recommended daily amount in many countries. They point out that vitamin C helps activate several enzymes in the body which enhance levels of metabolic energy and neurochemicals in the brain.
(Mood Improvement in Young Adult Males following Supplementation with Gold Kiwifruit, a High-Vitamin C Food. Journal of Nutritional Science (2013), vol. 2, e24.)