Now, researchers from New Zealand have discovered that daily kiwifruit supplementation may improve vitality and mood within as little as four days.
Their industry-funded study, which was published in the British Journal of Nutrition, also found that kiwifruit consumption led to improved flourishing.
Co-author Professor Tamlin Conner, from the University of Otago, said the findings provided a tangible, accessible way for people to support their mental wellbeing via their diet.
“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,” he said.
Not only are the findings novel, so was the methodology used to collect them: this was the first study to use intensive smartphone surveys to model the day-to-day timecourse of mood-related outcomes following vitamin C intervention.
This “highlights the value of using smartphone surveys to reveal the temporal changes in mood-related outcomes following nutrient supplementation”, the researchers concluded.
Vitamin C: A known mood-booster
However, research exploring how quickly mood improvements occur, whether after introducing vitamin C supplements or whole food sources, is limited.
This study, which was funded by the University of Otago and Zespri International Limited, the world's largest marketer of kiwifruit, aimed to fill that gap by studying the effects of an eight-week dietary intervention in 155 adults with low vitamin C levels.
Participants were supplemented with 250 mg daily vitamin C, a placebo, or two kiwifruit. They then reported their vitality, mood, flourishing, sleep quality, sleep quantity, and physical activity via smartphone surveys.
Daily kiwifruit improved participants’ vitality and mood
Kiwifruit supplementation improved vitality and mood within just four days, with effects peaking at around 14-16 days, and improved flourishing from day 14.
Vitamin C supplements, by comparison, 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 occur contributes to our 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,” he added. “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.”
While vitamin C tablets demonstrated some benefits, the study underscored the potential synergistic effects of consuming whole foods like kiwifruit, Fletcher explained.
“We encourage a holistic approach to nutrition and well-being, incorporating various nutrient-rich foods into your diet,” he said.
In addition to the implications for individuals seeking to improve their mental wellbeing, the researchers highlighted how the study introduces a novel methodology in nutritional research.
Conner said: “The use of intensive smartphone surveys offers a real-time understanding of the day-to-day changes in mood-related outcomes.”