Vitamin C (Ascorbic Acid) Deficiency and Excess

Dietary Needs and Sources of Vitamin C

Humans depend on dietary sources for vitamin C. An adequate intake is 40 mg for ages 0-6 mo and 50 mg for 6-12 mo. For older children the recommended dietary allowance is 15 mg for ages 1-3 yr, 25 mg for 4-8 yr, 45 mg for 9-13 yr, and 65-75 mg for 14-18 yr. The recommended dietary allowances during pregnancy and lactation are 85 mg/day and 120 mg/day, respectively. The requirement for vitamin C is increased during infectious and diarrheal diseases. Children exposed to smoking or environmental tobacco smoke also require increased amounts of foods rich in vitamin C. The best food sources of vitamin C are citrus fruits and fruit juices, peppers, berries, melons, guava, kiwifruit, tomatoes, cauliflower, and green leafy vegetables. Vitamin C is easily destroyed by prolonged storage, overcooking, and processing of foods.

Absorption of vitamin C occurs in the upper small intestine by an active process or by simple diffusion when large amounts are ingested. Vitamin C is not stored in the body but is taken up by all tissues; the highest levels are found in the pituitary and adrenal glands. The brain ascorbate content in the fetus and neonate is markedly higher than the content in the adult brain, a finding probably related to its function in neurotransmitter synthesis.

When a mother's intake of vitamin C during pregnancy and lactation is adequate, the newborn will have adequate tissue levels of vitamin C related to active placental transfer, subsequently maintained by the vitamin C in breast milk or commercial infant formulas. Breast milk contains sufficient vitamin C to prevent deficiency throughout infancy. Infants consuming pasteurized or boiled animal milk are at significant risk of developing deficiency if the other sources of vitamin C are also lacking in the diet. Neonates whose feeding has been delayed because of a clinical condition can also have ascorbic acid deficiency. For patients receiving total parenteral nutrition (TPN), 80 mg/day is recommended for full-term infants and 25 mg/kg/day for preterm infants. Parents and children who choose a limited (selective) diet or those on fad diets are at risk for vitamin C deficiency.

Vitamin C Deficiency

A deficiency of vitamin C results in the clinical presentation of scurvy . Children fed predominantly heat-treated (ultrahigh-temperature or pasteurized) milk or unfortified formulas and not receiving fruits and fruit juices are at significant risk for symptomatic disease. Infants and children on highly restrictive diets, devoid of most fruits and vegetables, are at risk of acquiring severe vitamin C deficiency. Such diets are occasionally promoted with unsubstantiated claims of benefit in autism and other developmental disorders, In scurvy, there is defective formation of connective tissues and collagen in skin, cartilage, dentine, bone, and blood vessels, leading to their fragility. In the long bones, osteoid is not deposited by osteoblasts, cortex is thin, and the trabeculae become brittle and fracture easily.