Recommended intakes and bioavailability
The current New Zealand recommended dietary intake for vitamin C is 45 mg/d. However, this intake is not sufficient to provide adequate plasma concentrations (i.e. 50 µmol/L). Intakes of at least 100-200 mg/d are required for adequate to optimal plasma vitamin C concentrations.
Although animal studies have shown that food-derived vitamin C can be taken up into the body more readily than synthetic vitamin C, our human studies have shown that food-derived and synthetic vitamin C have similar uptake into the body i.e. comparable bioavailability.
Clinical studies
- Marginal ascorbate status (hypovitaminosis C) results in an attenuated response to vitamin C supplementation
- Consumption of vitamin C is below recommended daily intake in many cancer patients and healthy volunteers in Christchurch
- Human skeletal muscle ascorbate is highly responsive to changes in vitamin C intake and plasma concentrations
- A randomized cross-over pharmacokinetic bioavailability study of synthetic versus kiwifruit-derived vitamin C
- A randomized steady-state bioavailability study of synthetic versus natural (kiwifruit-derived) vitamin C
- Bioavailability of vitamin C from kiwifruit in non-smoking males: determination of ‘healthy’ and ‘optimal’ intakes
Review articles
- Synthetic or food-derived vitamin C are they equally bioavailable?
- The bioavailability of vitamin C from kiwifruit
Infection and immune function
Patients with severe infections such as pneumonia and sepsis have decreased vitamin C levels due to enhanced requirement for the vitamin during infection and inflammatory conditions. Vitamin C supports the cardiovascular and immune systems and has important roles to play in immune cell function.
Clinical studies
- Hypovitaminosis C and vitamin C deficiency in critically ill patients despite recommended enteral and parenteral intakes
- Enhanced human neutrophil vitamin C status, chemotaxis and oxidant generation following dietary supplementation with vitamin C-rich SunGold kiwifruit
- Parenteral vitamin C relieves chronic fatigue and pain in a patient with rheumatoid arthritis and mononeuritis multiplex secondary to CNS vasculitis
Review articles
- The role of vitamin C in the treatment of pain: new insights
- Vitamin C and immune function
- The roles of vitamin C in skin health
- Ascorbate-dependent vasopressor synthesis: a rationale for vitamin C administration in severe sepsis and septic shock?
- The role of oxidants and vitamin C on neutrophil apoptosis and clearance
Cancer therapy and quality of life
New mechanisms of action of vitamin C are emerging which could play a role in cancer therapy and quality of life. Intravenous administration of vitamin C bypasses the regulated uptake of vitamin C through the intestines and provides significantly higher plasma concentrations.
Clinical studies
- Relief from cancer chemotherapy side effects with pharmacologic vitamin C
- Parenteral vitamin C for palliative care of terminal cancer patients
Preclinical studies
- Increased tumor ascorbate is associated with extended disease-free survival and decreased hypoxia-inducible factor-1 activation in human colorectal cancer
- Low ascorbate levels are associated with increased hypoxia-inducible factor-1 activity and an aggressive tumor phenotype in endometrial cancer
Review articles
- Ascorbate as a co-factor for Fe- and 2-oxoglutarate dependent dioxygenases: physiological activity in tumor growth and progression
- Regulation of the 2-oxoglutarate-dependent dioxygenases and implications for cancer
- The role of vitamin C in the treatment of pain: new insights
- The effect of intravenous vitamin C on cancer- and chemotherapy-related fatigue and quality of life
Metabolic health and diabetes
We have carried out observational studies investigating the associations of vitamin C with various aspects of human health and disease.
Clinical studies
- Inadequate vitamin C status in prediabetes and Type 2 diabetes mellitus: associations with glycaemic control, obesity, and smoking
- Vitamin C status correlates with markers of metabolic and cognitive health in 50 year olds: findings of the CHALICE cohort study
Mental health
The brain has a high requirement for vitamin C and the vitamin is a co-factor for the synthesis of a number of neurotransmitters and neuropeptide hormones with roles in mood and energy. The earliest symptoms of the vitamin C deficiency disease scurvy are fatigue, lethargy and depression.
