Ascorbic Acid: Physiological Roles and Dietary Considerations

Physiological Functions of Ascorbic Acid

Ascorbic acid, commonly known as vitamin C, is a water-soluble vitamin that plays a crucial role in various bodily functions. It is a potent antioxidant, protecting cells from damage caused by free radicals. It is essential for collagen synthesis, a protein that provides structure to skin, tendons, ligaments, and blood vessels. Ascorbic acid also enhances the absorption of non-heme iron from plant-based foods and is involved in the synthesis of certain neurotransmitters and hormones.

Ascorbic Acid Metabolism and Bioavailability

Ascorbic acid is absorbed in the small intestine via both active transport and passive diffusion. Absorption efficiency decreases with increasing intake. The body does not store ascorbic acid, and excess amounts are excreted in the urine. Bioavailability is affected by factors such as dosage, food matrix, and individual health status.

Dietary Sources of Ascorbic Acid

Excellent sources of ascorbic acid include fruits and vegetables, particularly citrus fruits (oranges, grapefruits, lemons, limes), berries (strawberries, blueberries, raspberries), tomatoes, peppers (especially bell peppers), broccoli, spinach, and kale. Some foods are fortified with ascorbic acid.

Factors Influencing Ascorbic Acid Needs

Several factors can influence an individual's requirement. These include age, sex, pregnancy, lactation, smoking status, and certain medical conditions. Smokers, for example, require more ascorbic acid than nonsmokers due to increased oxidative stress.

Consequences of Ascorbic Acid Deficiency

Severe deficiency of ascorbic acid leads to scurvy, a condition characterized by fatigue, weakness, joint pain, bleeding gums, and impaired wound healing. Marginal deficiency may contribute to impaired immune function and increased risk of chronic diseases.

Tolerable Upper Intake Level and Potential Risks of Excess

The Tolerable Upper Intake Level (UL) for ascorbic acid is established to prevent adverse effects from excessive intake. High doses of ascorbic acid can cause gastrointestinal disturbances such as diarrhea, nausea, and abdominal cramps. In individuals with certain conditions, such as hemochromatosis, high doses of ascorbic acid may exacerbate iron overload.