Kiwifruits and Vitamin C Benefits
Professor Margreet Vissers
University of Otago, New Zealand
Vitamin C is essential for life, and humans obtain this nutrient exclusively through the diet. It functions inside the cells in our bodies, where it plays an important role in supporting many essential processes. In the past decade, we have learned a great deal about the myriad of biological roles assigned to this micronutrient and this information has given us new insight and understanding of its vital importance to health maintenance and disease prevention.
The bioavailability of vitamin C to the tissues is determined by absorption through the gut, active uptake into the tissues via the circulation and clearance from the kidneys. Tissue saturation is achieved with plasma vitamin C levels of around 80 µM, which is similar to the levels maintained in animals that are able to synthesise the vitamin. Recent evidence suggests that tissue saturation best supports a number of important cell functions, including the regulation of oxidative metabolism, cell stress responses, hormone synthesis, epigenetic regulation, and life and death signalling pathways.
Higher vitamin C intake has been linked to improved wound healing, immune function and a decreased incidence of chronic diseases such as cardiovascular disease, diabetes and cancer. In addition, it has also been linked to improved mood and well-being, skin tone and to increased life expectancy. In the light of this knowledge, the recommended daily intake is being raised in a number of countries as a means of improving health and off-setting chronic diseases.
Many of the established and newly identified roles of vitamin C are associated with its ability to act as a co-factor for metal-containing enzymes that have important roles in the body.
These enzymes have functions that include: response to metabolic and oxygen stress (such as in diabetes and general illness); promoting the growth and progression of cancer; and stimulating immune function and wellbeing. Recent research has identified new members of the 2-oxoglutarate dependent dioxygenase family of enzymes that are involved in numerous biological functions including epigenetic regulation, hormone synthesis, angiogenesis and cell stress responses. The health implications of these discoveries will underpin future dietary and nutritional advice and, in particular, will improve our understanding of the need for optimal vitamin C intake on a daily basis.
Most people do not consume enough fresh fruit and vegetables to maintain saturating plasma levels of vitamin C, and available population statistics have indicated that, although acute scurvy is relatively uncommon, a significant proportion of western populations have low plasma status. In addition, vitamin C is rapidly depleted when a person is unwell, and this is an under-appreciated problem. We have investigated the effect of adding kiwifruit, an exceptional dietary source of vitamin C, to the daily diet. We have found that plasma and tissue saturation can easily be achieved and maintained by the addition of two kiwifruit per day.
View presentation Overview of the Health Benefits of Vitamin C by Prof Margreet Vissers from Kiwifruit Symposium