Do kiwifruits improve mood?

I came across a paper that attracted some attention, claiming that kiwifruit consumption could enhance mental health in just four days, so I decided to take a closer look to see if there were any valuable insights.

The study was published in the British Journal of Nutrition, authored by Fletcher et al., from New Zealand institutions. The research aimed to investigate the impact of vitamin C-rich foods, particularly kiwifruit, on mood outcomes over a short period.

There were two notable flaws in the randomisation process. First, group randomisation was employed, potentially introducing bias, as participants were segregated based on scheduled clinic visits. Secondly, a delay in tablet delivery led to non-random allocation across the intervention groups. These deviations from proper randomisation undermined the study's validity.

The study recruited 155 participants with low vitamin C levels, predominantly from higher education campuses in Dunedin, New Zealand. The intervention spanned four weeks, with participants assigned to consume either a vitamin C tablet, a placebo tablet, or two SunGold® kiwifruit daily. While blinding was maintained in the tablet arms, the nature of the kiwifruit intervention precluded blinding.

Analysis of the intervention's effects on participants' vitality, mood, flourishing, and sleep quality revealed no significant differences between the vitamin C tablet and placebo groups. Notably, while initial observations suggested marginal improvements in vitality and mood disturbance among kiwifruit consumers, these effects disappeared upon adjustment for confounding factors such as sleep, exercise, age, and ethnicity.

The headline claims should not have been made.

While the authors declared no conflicts, the study was funding by Zespri International Ltd., the world's largest marketer of kiwifruit. Really?!

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