Vitamin C is a water-soluble vitamin, antioxidant, and essential co-factor for collagen biosynthesis, carnitine and catecholamine metabolism, and dietary iron absorption. Humans are unable to synthesize vitamin C, so it is strictly obtained through dietary intake of fruits and vegetables. Citrus fruits, berries, tomatoes, potatoes, and green leafy vegetables are excellent sources of vitamin C. Although most vitamin C is completely absorbed in the small intestine, the percentage of absorbed vitamin C decreases as intraluminal concentrations increase. Proline residues on procollagen require vitamin C for the hydroxylation, making it necessary for the triple-helix formation of mature collagen. The lack of a stable triple-helical structure compromises the integrity of the skin, mucous membranes, blood vessels, and bone. Consequently, a deficiency in vitamin C results in scurvy, which presents with hemorrhage, hyperkeratosis, and hematological abnormalities.
Vitamin C deficiency usually arises in the setting of decreased intake or increased requirements or losses. Persons at risk for inadequate intake of vitamin include patients in the following groups:
Vitamin C is indicated to prevent and treat scurvy. Scurvy develops 1 to 3 months after initiating a vitamin C-deficient diet. Individuals may complain of lethargy, fatigue, malaise, emotional lability, arthralgias, weight loss, anorexia, and diarrhea. They also may experience easy bleeding, bruising, and poor wound healing. The cutaneous manifestations of scurvy include phrynoderma, corkscrew hairs, perifollicular hemorrhage and purpura, edema of the lower extremities, and splinter hemorrhages. Phrynoderma, or enlarged hyperkeratotic hair follicles, initially present on the posterolateral arms. This subsequently generalizes to involve the buttocks, posterior thighs, calves, shins, and back. Corkscrew hairs represent fractured and coiled hairs due to impaired keratin cross-links by disulfide bonds. With time, significant vascular congestion occurs, particularly in the lower extremities, leading to perifollicular hemorrhage and edema. This purpura is occasionally palpable, mimicking a cutaneous vasculitis. Blood vessel wall fragility also results in splinter hemorrhages of the nail bed. Oral disease is prominent among those with pre-existing poor dentition. Individuals may develop a hemorrhagic gingivitis, where the gingiva is initially red, swollen, and shiny and later becomes purple, necrotic, and prone to bleeding. Additionally, poorly formed soft teeth are prone to infection. Musculoskeletal disease is frequently seen in children. Hemorrhage can be intramuscular, intra-articular, or subperiosteal, leading to pain and pseudoparalysis. Bowing of the long bones, depression of the sternum, and swelling of the costochondral junctions are noted on physical examination. Radiographic findings include a transverse metaphyseal radiolucent band (scurvy line or Trummerfeld zone), widening at the zone of calcification (white line of Frankel), a ring of increased density around the epiphysis (Wimberger ring) and metaphyseal spurs with marginal fractures (Pelkan spurs). Conjunctival, intraocular, intracerebral, and gastrointestinal bleeding have been reported.
Daily need increases in patients with conditions like gingivitis, asthma, glaucoma, collagen disorders, heat stroke, arthritis, infections (pneumonia, sinusitis, rheumatic fever), and chronic illnesses. Hemovascular disorders, burns, and delayed wound healing are causes for an increase in the daily intake.
Absorption is through an energy-dependent process that has two mechanisms: simple diffusion and active transport. Two transporters are involved: SVCTs (sodium-dependent vitamin C transporters) and hexose transporters. The site for absorption is the distal small intestine and is regulated by renal excretion. Usual dietary doses of up to 100 mg/day are almost completely absorbed. The greatest concentrations of ascorbic acid are found in the pituitary gland, the adrenal gland, the brain, leukocytes, and eyes.
Ascorbic acid functions as the cofactor, enzyme complement, co-substrate and a very strong anti-oxidant in a variety of reactions and metabolic processes. It also stabilizes vitamin E and folic acid and enhances iron absorption. It neutralizes free radicals and toxins as well as attenuates inflammatory response, including sepsis syndrome.
Usually administered orally, the drug may be administered intramuscularly, intravenously (IV), or subcutaneously when malabsorption is suspected. For IV injection, minimize adverse reactions by diluting the drug with normal saline or glucose.
The average protective adult dose of vitamin C is 70 to 150 mg daily. Increase the dose to 300 mg to 1 g daily when scurvy is present.
Adverse effects include headaches, flushing, nausea or vomiting, and dizziness (IV use). Migraine headaches have been reported with a daily dose of 6 g.
Significant amounts of vitamin C can increase the risk of kidney stones and elevate uric acid and oxalate because it acidifies urine.
Vitamin C supplementation is contraindicated in blood disorders like thalassemia, G6PD deficiency, sickle cell disease, and hemochromatosis. Avoid taking supplements immediately before or following angioplasty. Diabetic patients should take vitamin C supplements with care as it raises blood sugar levels.
Vitamin C should be used cautiously in oxalate nephropathy or nephrolithiasis as acidification by ascorbic acid increases the chances of precipitation of cysteine, urate, and oxalate stones.
Scurvy is largely a clinical diagnosis. Serum ascorbic acid levels may be measured (greater than 11 micromoles/L), but this typically reflects recent dietary intake. Measurement of leukocyte ascorbic acid levels tends to be more accurate, but testing is not widely available. Normochromic normocytic anemia is common due to blood loss, folate deficiency, and iron deficiency.
Test dichlorophenolindophenol to measure vitamin C level in urine and serum/plasma and high-performance liquid chromatography (HPLC) to measure storage level in lymphocytes and tissues.
The recommended daily intake of vitamin C is 40 to 120 mg, depending on age and gender.
Scurvy is treated with ascorbic acid 100 to 300 mg daily until symptoms remit. Clinical improvement is noted within the first 1 to 2 weeks, with a resolution of fatigue, joint swelling, ecchymoses, and gingiva healing. Complete recovery frequently occurs within 3 months.
Vitamin C (in grams) can give false negative stool guaiac results and is rarely associated with fatal cardiac arrhythmias in patients with iron overload.