Health and Immune Function Benefits of Kiwifruit-derived Vitamin C
Dr Anitra C. Carr
University of Otago, New Zealand
Vitamin C is an essential micronutrient. Unlike most animals, we have lost the ability to synthesise our own vitamin C and must therefore obtain it from our diet. Fresh fruit and vegetables are the best source of vitamin C, and regular and adequate daily intake of vitamin C is required to prevent marginal vitamin C status (hypovitaminosis C) and the potentially fatal deficiency disease scurvy. Kiwifruit are an outstanding source of vitamin C with one kiwifruit providing twice the Recommended Dietary Intake (RDI) of vitamin C. We believe that vitamin C levels significantly higher than the current New Zealand RDI of 40 mg/day vitamin C are required for optimal health.
We have carried out several human intervention studies investigating the bioavailability of kiwifruit-derived vitamin C. We found that consumption of as little as half a gold kiwifruit per day was sufficient to significantly increase plasma vitamin C levels, and two gold kiwifruit per day (which constitutes ~200 mg/day vitamin C) provided optimal plasma levels. Few other food sources provide this benefit. We also showed an improvement in muscle, seminal fluid and white cell vitamin C status following kiwifruit intake. In addition, the intake of two kiwifruit per day was associated with improved wellbeing.
Vitamin C has a number of important functions in the body, from acting as a potent antioxidant, to its role as a cofactor for numerous biosynthetic and regulatory enzymes. We are particularly interested in its potential immune function benefits, in particular its effects on white blood cell function. White blood cells, such as neutrophils, are our first line of defence against invading microorganisms. Neutrophils migrate towards sites of infection, engulf (or phagocytose) bacteria and then produce an array of compounds, such as reactive oxidants, to kill the bacteria. We have carried out a human intervention study to investigate the effects of kiwifruit supplementation on white cell function. We found a significant increase in neutrophil vitamin C status following supplementation with two gold kiwifruit per day and an increase in the ability of neutrophils to migrate and generate oxidants. Both of these functions would likely translate into better overall immune function and health.
Combined analysis of the data from our human intervention studies has indicated that people require vitamin C intakes significantly higher than the current New Zealand RDI to achieve optimal plasma levels. Therefore, we recommend a daily intake of 200 mg/day vitamin C which can be obtained from a daily diet of 5-7 servings of fruit and vegetables, provided that at least one of those is a high vitamin C food such as kiwifruit. This will provide optimal plasma and tissue vitamin C levels and enhanced health outcomes.
View Presentation on Kiwifruit and Vitamin C by Dr Anitra Carr from Kiwifruit Symposium