Ascorbic acid

Ascorbic acid is vitamin C, a water-soluble nutrient that humans must obtain from food or supplements. Unlike many animals, humans cannot synthesize vitamin C on their own. It is needed for collagen synthesis, tissue repair, immune function, antioxidant defense, carnitine metabolism, catecholamine metabolism, and improved absorption of non-heme iron from plant foods. Without enough vitamin C, connective tissue structure suffers.

The classic severe deficiency disease is scurvy, with bleeding gums, weakness, poor wound healing, bruising, pain, anemia, and connective tissue damage. Severe scurvy is less common today, but inadequate intake can occur with very limited diets, alcoholism, smoking, serious disease, malabsorption, eating disorders, and diets with almost no vegetables, greens, or fruit. A low-carbohydrate diet does not have to be low in vitamin C, but it can become low when food variety is too narrow.

Food sources

Rich vitamin C sources include bell peppers, broccoli, Brussels sprouts, cauliflower, cabbage, leafy greens, fermented cabbage, lemon, lime, kiwi, citrus fruit, strawberries, and other berries. For keto and LCHF, vegetables, greens, fermented cabbage, lemon juice, and modest portions of berries are usually easier to fit than juices, sweet fruits, and smoothies. The number per 100 grams is not the only issue. The actual serving and carbohydrate load matter.

Vitamin C is sensitive to prolonged storage, heat, and water. Boiling in a large volume of water and discarding the liquid can reduce content substantially. Gentler options include quick cooking, steaming, short braising, raw vegetables when tolerated, and fermented foods. This does not mean everything must be eaten raw. It means the diet should regularly include vitamin C sources rather than rely on an occasional slice of lemon.

Supplements and dose

Most adult requirements can be met with moderate amounts. In the United States, the recommended intake is 90 mg per day for men and 75 mg for women, and smokers need more because of higher oxidative stress. Supplements often contain 250, 500, or 1000 mg, but absorption does not rise in a straight line. The larger the single dose, the lower the retained fraction and the greater the chance of diarrhea, cramping, and bloating. Smaller divided doses or food-based intake may be more practical than one gram at once.

High-dose vitamin C is popular for colds, fatigue, and immune support, but its effects should not be exaggerated. Vitamin C is important for normal immune function, yet it is not a universal treatment for viral infections, cancer, or cardiovascular disease. If a person eats poorly, sleeps badly, smokes, has inadequate protein and iron, or has uncontrolled diabetes, a scoop of ascorbic acid powder will not fix the foundation of the problem.

Smoking increases vitamin C needs because it raises oxidative stress and uses antioxidant defenses faster. That does not mean a smoker can simply take more ascorbic acid and protect the arteries. Stopping tobacco remains far more important than any supplement, while vitamin C only covers one part of the nutrient requirement.

Keto, iron, and tolerance

On keto, vitamin C is often underestimated because attention goes to carbohydrates, ketones, and fats. Connective tissue, gums, vessel walls, skin, and wound healing still require adequate vitamin C. If the diet consists mostly of meat, butter, cheese, and very few vegetables, the risk of inadequate intake becomes real. A well-formulated low-carbohydrate diet can include peppers, cabbage, broccoli, greens, and tart berries without exceeding carbohydrate limits.

Ascorbic acid improves absorption of non-heme iron, which can be useful in iron deficiency, especially when iron comes from plant foods. In hemochromatosis, iron overload, or a tendency toward high ferritin and transferrin saturation, high doses require caution. In susceptible people, large doses may also increase oxalate burden and may be undesirable with kidney stone history. The practical conclusion is simple: vitamin C deficiency should be corrected, but megadoses should have a reason, tolerability, and awareness of risk.