A University of Otago study shows the furry fruit is a powerful mood booster and can improve vitality and mental wellbeing in as little as four days.
Co-author and psychologist Professor Tamlin Conner said the findings provided a tangible and accessible way for people to support their mental health.
"It’s great for people to know that small changes in their diet, like adding kiwifruit, could make a difference in how they feel every day."
Vitamin C intake has been associated with improved mood, vitality, wellbeing and lower depression, while vitamin C deficiency has been associated with higher depression and cognitive impairment.
However, Prof Conner said limited research had assessed how quickly mood improvements occurred after introducing vitamin C supplements or whole food sources.
The researchers aimed to fill that gap with an eight-week dietary intervention of 155 adults with low vitamin C.
Daily, participants took either a vitamin C supplement, placebo or two kiwifruit.
They then reported their vitality, mood, flourishing, sleep quality, sleep quantity and physical activity using smartphone surveys.
The researchers found kiwifruit supplementation improved vitality and mood within four days, peaking around 14-16 days, and improved flourishing from day 14.
Vitamin C, on the other hand, marginally improved mood until day 12.
Lead author Dr Ben Fletcher, who conducted the research as part of his PhD at Otago, said understanding the nuances of when and how these effects occurred day-to-day, contributed to knowledge of the potential benefits of vitamin C-rich foods and supplements on mental health.
"This helps us see that what we eat can have a relatively fast impact on how we feel.
"Our participants had relatively good mental health to begin with so had little room for improvement, but still reported the benefits of kiwifruit or vitamin C interventions."
He said while vitamin C tablets provided some improvements, the study underscored the potential synergistic effects of consuming whole foods like kiwifruit.
"We encourage a holistic approach to nutrition and wellbeing, incorporating various nutrient-rich foods into your diet."
