Research Summary
Vitamin C in humans must be ingested for survival. As an electron donor, vitamin C acts as a potent water-soluble antioxidant. This property underlies all of its known functions. The antioxidant effects of vitamin C have been demonstrated in numerous in vitro experiments. Human diseases such as atherosclerosis and cancer might partially result from oxidant damage to tissues. Oxidation of lipids, proteins, and DNA leads to specific oxidation products that can be measured in laboratory settings. While these biomarkers of oxidation have been measured in humans, the assays used are neither validated nor standardized, and the connection between oxidant markers and human disease conditions remains unclear.
Epidemiological studies indicate that diets rich in fruits and vegetables are associated with lower risks of cardiovascular disease, stroke, and cancer, as well as increased longevity. However, it is uncertain whether these protective effects can be directly attributed to vitamin C. Intervention studies using vitamin C have not shown changes in markers of oxidation or significant clinical benefits. Dose concentration studies of vitamin C in healthy individuals demonstrated a sigmoidal relationship between oral doses and plasma or tissue vitamin C concentrations, emphasizing the importance of optimal dosing in intervention studies.
Future studies on the antioxidant actions of vitamin C should ideally focus on selected patient groups. These groups should either have increased oxidative damage, as determined by reliable biomarkers, or suffer from diseases with high morbidity and mortality rates that are thought to be caused or exacerbated by oxidant damage.
Key teaching points:
- Vitamin C is essential for survival and is a powerful water-soluble antioxidant.
- Antioxidant actions of vitamin C have been demonstrated through in vitro experiments.
- Oxidant damage to biological molecules results in measurable oxidation products, though these assays are not yet fully validated.
- Diets high in fruits and vegetables are associated with lower risks of cardiovascular disease and cancer, but it is unclear whether vitamin C plays a direct role in these benefits.
- There is a sigmoidal relationship between oral doses of vitamin C and plasma concentrations, with excess vitamin C being excreted from the body.
- Beyond preventing scurvy, vitamin C has no proven clinical benefits in humans, and its treatment has not led to significant changes in biomarkers of oxidation or clinical outcomes.
Keywords: ascorbic acid, oxidation, diet, low-density lipoproteins
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