Vitamin C

Vitamin C is an essential nutrient found in fruits and vegetables that your body cannot make on its own. It helps build and repair tissues, supports your immune system, and acts as an antioxidant to protect your cells. Low levels—most often caused by a diet low in fresh produce or by smoking—can lead to symptoms like easy bruising, bleeding gums, fatigue, and slow wound healing. Most people get enough vitamin C through a balanced diet, and taking very large amounts in supplement form is generally not necessary and may cause kidney stones in some people. Your healthcare provider can help interpret your results in the context of your diet, lifestyle, and any symptoms you may have.

When elevated: Elevated plasma vitamin C levels are generally not associated with adverse clinical outcomes at physiologic ranges. Very high levels resulting from excessive supplementation may increase urinary oxalate excretion, potentially raising the risk of calcium oxalate kidney stones in predisposed individuals. High-dose intravenous ascorbic acid can interfere with certain point-of-care glucose monitoring systems. When low: Low vitamin C levels indicate inadequate tissue stores and are associated with impaired collagen synthesis, poor wound healing, increased capillary fragility, and immune dysfunction. Frank deficiency (scurvy) presents with perifollicular hemorrhages, corkscrew hairs, gingival bleeding, and fatigue. Subclinical deficiency may contribute to increased oxidative stress and impaired iron absorption.

Vitamin C supports collagen synthesis and immune function, both important for tissue repair after training and reducing infection risk during heavy training blocks. Athletes with high oxidative stress from intense exercise may benefit from adequate intake, though supplementation beyond dietary sources lacks strong evidence for performance enhancement in well-nourished individuals.