Food Supplements and Vitamins. Vitamin C (ascorbic acid)

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Background

Vitamin C (ascorbic acid) is a water-soluble vitamin, which is needed by the body to form collagen in bones, cartilage, muscle, and blood vessels, and which aids in the absorption of iron. Dietary sources of vitamin C include fruits and vegetables, particularly citrus fruits such as oranges.

Severe deficiency of vitamin C causes scurvy. Although rare, scurvy includes potentially severe consequences and can cause sudden death. Patients with scurvy are treated with vitamin C and should be under medical supervision.

Many uses for vitamin C have been proposed, but few have been found to be beneficial in scientific studies. In particular, research on asthma, cancer, and diabetes remains inconclusive, and no benefits have been found for the prevention of cataracts or heart disease.

The use of vitamin C in the prevention or treatment of the common cold and respiratory infections remains controversial, with research ongoing. For cold prevention, more than 30 clinical trials including over 10,000 participants have examined the effects of taking daily vitamin C. Overall, no significant reduction in the risk of developing colds has been observed. In people who developed colds while taking vitamin C, no difference in the severity of symptoms has been seen overall, although a small, significant reduction in the duration of colds has been reported (approximately 10% in adults and 15% in children). Notably, some studies of people living in extreme circumstances, including soldiers in subarctic exercises, skiers, and marathon runners, have found a significant reduction in the risk of developing a cold, by approximately 50%. This area merits additional research and may be of particular interest to elite athletes or military personnel. For cold treatment, numerous studies have examined the effects of starting vitamin C after the onset of cold symptoms. So far, significant benefits have not been observed.

Dosing

NB! The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (over 18 years old)

The recommended daily intake by the U.S. Food and Nutrition Board of the Institute of Medicine for men more than 18 years old is 90 milligrams daily; for women more than 18 years old, it is 75 milligrams daily; for pregnant women more than 18 years old, it is 85 milligrams daily; and for breastfeeding women more than 18 years old, it is 120 milligrams daily. 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 milligrams daily has been recommended by some.

The upper limit of intake (UL) should not exceed 2,000 milligrams daily in men or women more than 18 years old (including pregnant or breastfeeding women).

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

  • For treating the common cold, 1-3 grams daily has been used. For preventing the common cold in people under physical stress, 600-1,000 milligrams of vitamin C daily has been used. During acute stress, one gram of vitamin C three times daily, as a sustained-release preparation, has been used for up to 14 days.
  • For preventing contrast-mediated nephropathy, three grams of vitamin C is given before coronary angiography and then two grams is given after the procedure, in the evening and again the following morning. For chronic hemodialysis in adults, 100-200 milligrams daily has been used.
  • For preventing nitrate tolerance, 3-6 grams of vitamin C has been used daily.
  • For treatment of premalignant gastric lesions, one gram of vitamin C has been used twice daily.
  • For infertility associated with luteal phase defect, 750 milligrams of vitamin C has been used daily.
  • For preventing complex regional pain syndrome in patients with wrist fractures, 500 milligrams of vitamin C daily for 50 days has been used.
  • For preventing gout, 500-1,500 milligrams of vitamin C daily from food and/or supplements has been used.
  • For high blood pressure, the median vitamin C dose and study duration has been 500 milligrams daily and six weeks, respectively.
  • Most topical preparations used for aged or wrinkled skin are applied daily and may contain 5-10% vitamin C.

Children (under 18 years old)

The recommended daily intake by the U.S. Food and Nutrition Board of the Institute of Medicine for infants 0-12 months old is human milk content (older recommendations specified 30-35 milligrams); for children 1-3 years old, it is 15 milligrams; for children 4-8 years old, it is 25 milligrams; for children 9-13 years old, it is 45 milligrams; and for adolescents 14-18 years old, it is 75 milligrams for boys and 65 milligrams for girls. The tolerable upper intake levels (UL) for vitamin C are 400 milligrams daily for children 1-3 years old; 650 milligrams daily for children 4-8 years old; 1,200 milligrams daily for children 9-13 years old; and 1,800 milligrams daily for adolescents and pregnant and lactating women 14-18 years old.

For scurvy or vitamin C deficiency in children, 100-300 milligrams of vitamin C daily by mouth in divided doses for two 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 seven days. Treatment should be under strict medical supervision.

For tyrosinemia in premature infants on high-protein diets, 100 milligrams of vitamin C has been used.

Safety

NB! There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

Avoid if sensitive or allergic to any ingredients present in Vitamin C products.

Side Effects and Warnings

Vitamin C is generally regarded as safe in amounts normally 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 of vitamin C have been associated with multiple adverse effects. These include kidney stones, severe diarrhea, nausea, and gastritis. Rarely, flushing, faintness, dizziness, and fatigue have been noted. In cases of toxicity due to massive ingestions of vitamin C, forced fluids, and diuresis may be beneficial. In postmenopausal women with diabetes, supplemental vitamin C in doses greater than 300 milligrams daily has been associated with increased risk of heart-related death.

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 extra vitamin C throughout their pregnancy.

Vitamin C in high doses appears to interfere with the blood-thinning effects of anticoagulants such as warfarin by lowering prothrombin time (PT). Caution is advised in patients with bleeding disorders or those taking drugs that affect bleeding. Dosing adjustments may be necessary.

Vitamin C may affect blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Use cautiously in patients with cancer, glucose-6-phosphate dehydrogenase deficiency, anemia and related conditions, kidney stones, or sickle cell disease, or after angioplasty. Use cautiously in patients taking antibiotics, anticancer agents, HIV medications, barbiturates, estrogens, fluphenazine, or iron supplements. Use parenteral (injected) vitamin C cautiously, as it may cause dizziness, faintness, or injection site discomfort, and in high doses, it may lead to renal insufficiency (kidney function problems).

Avoid in patients with known allergies or hypersensitivities to any ingredients in Vitamin C products. Avoid high doses of vitamin C in people with conditions aggravated by acid loading, such as cirrhosis, gout, renal tubular acidosis, or paroxysmal nocturnal hemoglobinuria. Avoid high doses of vitamin C in patients with kidney failure or in those taking agents that may damage the kidneys, due to an increased risk of kidney failure.

Pregnancy and Breastfeeding

Vitamin C intake from food is generally considered safe during pregnancy. It is not clear if vitamin C supplementation in amounts exceeding Dietary Reference Intake recommendations is safe or beneficial during pregnancy. There are rare reports of scurvy due to tolerance or resistance in infants born to mothers taking extra vitamin C throughout the pregnancy. The data are too few to say if vitamin C supplementation alone or combined with other supplements is beneficial during pregnancy. Preterm birth may increase with vitamin C supplementation.

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

source:  http://www.mayoclinic.com

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