Researchers at the University of Otago discovered that eating two kiwifruit (Actinidia deliciosa) revealed more marked findings when compared to a matched population taking vitamin C supplements.
Vitamin C has been associated with greater feelings of vitality, however, these associations have rarely been tested in randomized controlled trials. To test the effects of vitamin C on subjective vitality and whether these effects are driven by vitamin C, researchers conducted a placebo-controlled intervention.
To test whether increasing vitamin C through whole fruit or tablets can improve feelings of vitality, researchers recruited 167 participants between the ages of 18 to 35 who had low baseline levels of vitamin C.
The trial consisted of a two-week lead-in, four-week intervention, and two-week washout. Self-reported sleep quality and physical activity were measured every other day through smartphone surveys and nutritional confounds were assessed using a three-day food diary during each study phase. Additionally, Vitamin C levels in blood were measured fortnightly and participants filled out questionnaires to help gauge mood, fatigue, and well-being.
The participants were randomly divided into three groups: a kiwifruit group, an equivalent vitamin C tablet group (250 mg), or a placebo-tablet group.
Each day for four weeks, participants were asked to eat two Sungold kiwifruit, which are known to be exceptionally high in vitamin C, or consume a tablet.
The authors reported that “Participants consuming kiwifruit showed significantly improved mood and well-being during the intervention period; improvements in well-being were sustained during washout. Decreased fatigue and increased well-being were observed following intake of vitamin C alone, but only for participants with consistently low vitamin C levels during lead-in. Diet records showed that participants consuming kiwifruit reduced their fat intake during the intervention period. Intervention effects remained significant when adjusting for age and ethnicity, and were not explained by sleep quality, physical activity, BMI, or other dietary patterns, including fat intake.”
Results found that vitamin C levels in both the kiwifruit group and vitamin C tablet group increased to normal within two weeks, with no placebo effect reported.
"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," explained lead author Associate Professor Tamlin Conner.
It’s well-documented that vitamin C serves a number of functions and increases the production of many hormones and neurotransmitters. These include adrenalin, serotonin, and oxytocin, all of which control stress levels, regulate mood, and promote feelings of well-being.
Even though links between vitamin C and physical functioning are established, one of the study’s researchers, Professor Margreet Vissers, said this research establishes a role for vitamin C in mental functioning, with whole fruit intake promoting even more emotional benefits.
Growing evidence continues to highlight the importance of the gut–brain axis in regulating stress-related responses. Conner says by increasing vitamin C intake, people can get other active ingredients that will benefit the gut-brain axis and beyond.
"For example, kiwifruit has numerous additional vitamins and minerals that support health and are also high in dietary fiber, 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."
2020, 12(9), 2898; doi: 10.3390/nu12092898
"KiwiC for Vitality: Results of a Randomized Placebo-Controlled Trial Testing the Effects of Kiwifruit or Vitamin C Tablets on Vitality in Adults with Low Vitamin C Levels”
Authors: T. Conner et al.