Vitamin C : Dosing, Safety and Interactions

by MedlinePlus

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Dosing

Standardization:

Dosage forms: Vitamin C is available in multiple dosage forms including oral (regular or sustained release) and intravenous delivery. Oral forms include 100-1000mg capsules or tablets, powders, liquids/oral solutions (for example, 1-4g/5mL).

Food sources: Apples, asparagus, berries, broccoli, cabbage, melon (cantaloupe, honeydew, watermelon), cauliflower, citrus fruits (lemons, oranges), fortified breads/grains/cereal, kale, kiwi, potatoes, spinach, tomatoes.

Adults (18 years and older):

Dietary Reference Intakes (DRIs): Recommended daily intake by the U.S. Food and Nutrition Board of the institute of Medicine for men older than 18-years-old is 90 mg/day; for women older than 18-years-old is 75 mg/day; for pregnant women older than 18-years-old is 85 mg/day; for breastfeeding women older than 18-years-old is 120 mg/day. Recently, some experts have questioned whether the recommended daily intake should be raised. Others have recommended higher intake in some individuals, such as smokers, in whom an additional 35 mg/day has been recommended by some.

Upper limit of intake (UL): Should not exceed 2000 mg/day in men or women older than 18-years-old (including pregnant or breastfeeding women).

Scurvy/deficiency: Vitamin C administered by mouth or injection is effective for curing scurvy. In adults, 100-250 mg by mouth four times daily for 1 week is generally sufficient to improve symptoms and replete body vitamin C stores. Some experts have recommended 1-2 grams/day for 2 days followed by 500 mg/day for 1 week. Symptoms should begin to improve within 24-48 hours, with resolution within 7 days. Treatment should be under strict medical supervision. For asymptomatic vitamin C deficiency, lower daily doses may be used.

Plaque/calculus on teeth: Patients chewed five or 10 pieces of gum containing 60 mg of vitamin C per day for a period of 3 months in one study.

Prevention of premature rupture of chorioamniotic membranes: 100 mg of vitamin C per day has been studied.

Common cold prevention/treatment: For cold prevention, 200 mg/day or higher has been used. For cold treatment, up to 1000-2000 mg/day has been used.

Other: Dosing regimens of vitamin C with unproven effectiveness or safety include: 120-450 mg/day for antioxidant effects; 500-2000 mg prior to exercise for exercise-induced asthma prevention; 45-1000 mg/day for atherosclerosis prevention; 3000 mg/day for delayed-onset muscle soreness; 1000-2000 mg/day for diabetes; 50 mg/day for gastric ulcer; 300-3000 mg/day for high cholesterol; 200 mg/day for male infertility; 2000 mg/day for sunburn protection; 3-12 grams/day for urine acidification; 1000-1500 mg/day for wound healing.

Children (younger than 18 years):

Adequate Intakes (AIs) and U.S. Dietary Reference Intakes (DRIs): The AI for infants ages 0-6 months-old is 40 mg/day, and for infants 7-12 months-old is 50 mg/day. The DRI for children 1-3 years-old is 15 mg/day; for 4-8 years-old is 25 mg/day; for 9-13 years-old is 45 mg/day; for 14-18 year-old males is 75 mg/day; for 14-18 year-old females is 65 mg/day; for 14-18 year-old pregnant females is 80 mg/day; for 14-18 year-old breastfeeding females is 115 mg/day. Recently, some experts have questioned whether recommended daily intakes should be raised.

Tolerable Upper Intake Levels (UL): The UL has not been determined for infants ages 0-12 months, and vitamin C in this group should only be derived from food intake to avoid excess doses. The UL for children ages 1-3 years-old is 400 mg/day; the UL for ages 4-8 years-old is 650 mg/day; the UL for ages 9-13 years-old is 1200 mg/day; the UL for ages 14-18 years-old is 1800 mg/day (including pregnant or breastfeeding females).

Scurvy/deficiency: In children, 100-300 mg/day by mouth in divided doses for 2 weeks has been used. Older or larger children may require doses closer to adult recommendations. If vitamin C is not available, orange juice may be used for infantile scurvy. Symptoms should begin to improve within 24-48 hours, with resolution within 7 days. Treatment should be under strict medical supervision. For asymptomatic vitamin C deficiency, lower daily doses may be used.

Safety

Side Effects and Warnings

General: Vitamin C is generally regarded as safe in amounts obtained from foods. Vitamin C supplements are also generally regarded as safe in most individuals in recommended amounts, although side effects are rarely reported including nausea, vomiting, heartburn, abdominal cramps, and headache. Dental erosion may occur from chronically chewing vitamin C tablets.

High doses/toxicity: High doses of vitamin C have been associated with multiple adverse effects, particularly at doses greater than 2000 mg/day. These include kidney stones, severe diarrhea, nausea, and gastritis. Rarely, flushing, faintness, dizziness, and fatigue have been noted. Large doses may precipitate hemolysis (red blood cell destruction) in patients with glucose 6-phosphate dehydrogenase deficiency. High doses of vitamin C should be avoided in people with conditions aggravated by acid loading, such as cirrhosis, gout, renal tubular acidosis, or paroxysmal nocturnal hemoglobinuria. Parenteral (injected) vitamin C may cause dizziness, faintness, injection site discomfort, and in high doses may lead to renal insufficiency (kidney function problems). In cases of toxicity due to massive ingestions of vitamin C, forced fluids and diuresis may be beneficial.

Warnings: High doses of vitamin C should be avoided in patients with glucose 6-phosphate dehydrogenase deficiency, kidney stones, cirrhosis, gout, renal tubular acidosis, or paroxysmal nocturnal hemoglobinuria.

Tolerance/resistance: Healthy adults who take chronic large doses of vitamin C may experience low blood levels of vitamin C when they stop taking the high doses and resume normal intake. To avoid this potential complication, people who are taking high doses who wish to reduce their intake should do so gradually rather than acutely. There are rare reports of scurvy due to tolerance or resistance following cessation after long-term high-dose use, such as in infants born to mothers taking 400 mg/day or greater throughout their pregnancy.

Pregnancy and Breastfeeding

Pregnancy: Vitamin C intake from food is generally considered safe during pregnancy. However, it is not clear if vitamin C supplementation in amounts exceeding Dietary Reference Intake recommendations is safe or beneficial. There are rare reports of scurvy due to tolerance/resistance in infants born to mothers taking 400 mg/day or greater throughout their pregnancy.

Breastfeeding: Vitamin C is present in breastmilk. Vitamin C intake from food is generally considered safe in breastfeeding mothers. Limited research suggests that vitamin C in breastmilk may reduce the risk of the development of childhood allergies. It is not clear if vitamin C supplementation in amounts exceeding Dietary Reference Intake recommendations is safe or beneficial.

Interactions

Interactions with Drugs

Acetaminophen (Tylenol): Vitamin C may increase adverse effects associated with acetaminophen.

Antacids: Vitamin C may increase adverse effects associated with aluminum-containing antacids such as aluminum hydroxide (Maalox, Gaviscon).

Aspirin: Vitamin C may increase blood levels and adverse effects of aspirin, whereas aspirin may decrease blood levels of vitamin C.

Barbiturates: The effects of vitamin C may be decreased by barbiturates including phenobarbital (Luminal, Donnatal), pentobarbital (Nembutal), or secobarbital (Seconal).

Fluphenazine (Permitil, Prolixin): Vitamin C supplementation may decrease levels of the drug fluphenazine in the body.

HIV medications (protease inhibitors): Concomitant administration of high doses of vitamin C can reduce steady-state indinavir plasma concentrations.

Levodopa (Dopar, Larodopa): There is limited case report evidence that high dose vitamin C may reduce side effects of levodopa therapy such as nausea or malcoordination.

Nicotine: Nicotine products such as cigarettes, cigars, chewing tobacco, or nicotine patches may decrease the effects of vitamin C.

Oral contraceptives/estrogens: Oral estrogens may decrease the effects of vitamin C in the body. When taken together, vitamin C may increase blood levels of ethinyl estradiol.

Tetracyclines: The effects of vitamin C may be decreased by tetracycline antibiotics such as doxycycline (Vibramycin), minocycline (Minocin), or tetracycline (Sumycin).

Warfarin (Coumadin): Vitamin C in high doses appears to interfere with the blood thinning effects of warfarin by lowering prothrombin time (PT), as noted in case reports in the 1970s. Complications have not been reported (such as increased blood clots).

Interactions with Herbs and Dietary Supplements

Iron: When taken together, vitamin C may increase the absorption of iron in the gastrointestinal tract, although this effect appears to be variable and may not be clinically significant.

Lutein: Vitamin C may increase absorption of lutein vitamin supplements.

Vitamin B12 (cobalamin, cyanocobalamin): Large doses of vitamin C may interfere with the absorption and metabolism of vitamin B12.

Interactions with Laboratory Tests

Bilirubin: Vitamin C supplements may cause false increases in tests of blood bilirubin levels.

Carbamazepine levels: Vitamin C supplements may cause false increases in blood carbamazepine levels.

Creatinine: Vitamin C supplements may cause false increases in blood creatinine levels.

Glucose: Vitamin C supplements may interfere with the accuracy of blood glucose tests.

LDH (lactose dehydrogenase): Vitamin C may cause a false decrease in blood LDH levels.

Prothrombin time (PT): Vitamin C in high doses appears to interfere with the blood thinning effects of warfarin by lowering prothrombin time (PT), as noted in case reports in the 1970s. Complications have not been reported (such as increased blood clots).

SGOT (glutamic oxaloacetic transaminase): Vitamin C supplements may cause false increases in blood SGOT levels.

Stool occult blood (guaiac): Vitamin C supplements can cause false-negative stool occult blood tests, within 48-72 hours after vitamin C ingestion.

Theophylline levels: Vitamin C supplements may cause false decreases in blood theophylline levels.

Uric acid levels: Vitamin C supplements may cause false increases in blood uric acid levels.

Urinary acetaminophen (Tylenol): Vitamin C supplements can cause false-negative urine acetaminophen tests.

Urinary glucose: Vitamin C supplements can cause false-positive urinary glucose results with the cupric sulfate reagent test and false-negative urinary glucose results with the glucose oxidase test, within 48-72 hours after vitamin C ingestion.

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