Adults low in dietary vitamin C can improve their mood by eating two kiwifruit a day for two weeks, new research by Otago University has found.
The study was funded by kiwifruit marketing company Zespri, but was conducted independently.
A third of the 167 participants in the trial had to eat two Sungold kiwifruit a day for four weeks, while the second had to take vitamin C tablets and the third group were given placebo tablets.
Lead author, Associate Professor Tamlin Conner from the university's psychology department, said results showed vitamin C levels in both the kiwifruit group and vitamin C tablet group increased to normal within two weeks. There was no placebo effect.
But Conner said a key finding was that the group eating kiwifruit also reported improved feelings of vitality. The research highlighted the advantages of ingesting vitamin C through whole fruits, such as kiwifruit, she said.
"Whole fruit had a broader range of benefits; lessening fatigue and improving mood and well-being across a wider number of people than we saw in the supplement group.
"The vitamin C tablet did decrease fatigue and improve well-being to some extent for individuals with consistently low vitamin C levels leading up to the intervention. Interestingly, the benefits from consuming kiwifruit emerged in just two weeks."
Conner said by raising vitamin C levels through whole foods such as kiwifruit, people could get other active ingredients that would benefit more systems in the body and brain.
"For example, kiwifruit has numerous additional vitamins and minerals that support health and are also high in dietary fibre, which is beneficial to the gut. There are important links between the gut and the regulation of mood. This could account for why kiwifruit benefited mood more than vitamin C tablets."
Co-investigator, Professor Margreet Vissers, said while links between vitamin C and physical functioning were well-documented, this study established a role for vitamin C in mental functioning. The study also suggests that whole fruit intake promotes added benefits to mental function, she said.
Conner said the study was very tightly controlled; participants food consumption was tracked and their blood and vitamin C levels were monitored. Participants did not eat the skin of the kiwifruit during the study.
"We ruled out other kinds of possible explanations [for improved mood] so you can imagine that maybe people who ate the kiwifruit they started to feel better so maybe they started exercising too, that just wasn't the case."