News & tips on health, fitness and nutrition

Tuesday, January 28, 2014

Vitamin C (Ascorbic acid)


Vitamin C (ascorbic acid) is a water-soluble vitamin, which is necessary in the body to form collagen in bones, cartilage, muscle, and blood vessels, and 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. Scurvy is treated with vitamin C, and should be under medical supervision.

Many uses for vitamin C have been proposed, but few have been conclusively demonstrated as being beneficial in scientific studies. In particular, research in asthma, cancer, and diabetes remain inconclusive, while no benefits have been found in the prevention of cataracts or heart disease.


The use of vitamin C in prevention/treatment of the common cold and respiratory infections remains controversial, with ongoing research. 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 severity of symptoms has been seen overall, although a very small significant reduction in the duration of colds has been reported (approximately 10% in adults and 15% in children). Notably, a subset of studies in people living in extreme circumstances, including soldiers in sub-arctic exercises, skiers, and marathon runners, have reported a significant reduction in the risk of developing a cold of approximately 50%. This area merits additional study, 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. Overall, no significant benefits have been observed.


Synonyms


Antiscorbutic vitamin, ascorbate, ascorbic acid (AA), ascorbyl palmitate, calcium ascorbate, cevitamic acid, iso-ascorbic acid, l-ascorbic acid, sodium ascorbate.

Evidence
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.


Uses based on scientific evidenceGrade*
Vitamin C deficiency, scurvy


Causes: Scurvy is caused by a dietary deficiency of vitamin C. Although scurvy is uncommon, it may occur in malnourished individuals, those with increased vitamin C requirements (such as pregnant or breastfeeding women), or in infants receiving unsupplemented milk diets. There are rare reports of scurvy due to tolerance or resistance following long-term high-dose use, including infants born to mothers taking vitamin C throughout their pregnancy.Symptoms: Initial symptoms of scurvy in adults may include loss of appetite, diarrhea, shortness of breath, weakness, and fever, followed by irritability, depression, leg pain, pseudoparalysis, swelling over long bones of the body, anemia, paleness, poor wound healing, corkscrew hair, dry eyes, skin thickening (hyperkeratosis), and bleeding (particularly gum bleeding, bleeding behind the eyes causing prominence [proptosis], bleeding at the joints of the ribs and sternum causing discoloration under the skin of the chest [costochondral beading, scorbutic rosary], skin bruising, or blood in the urine or stool). In infants, symptoms may include irritability, thigh tenderness, pseudoparalysis, bleeding around the lower ends of the leg bones (femur and tibia) causing pain, and assumption of a frog-leg posture. If left untreated, scurvy can proceed to seizures, shock or sudden death.History: Scurvy has been described since ancient Egypt, and epidemics were witnessed during the 16th-18th Centuries, in particular among sailors. In the mid-1700s, the British naval surgeon James Lind discovered that oranges and lemons, both sources of vitamin C, are effective in preventing/curing scurvy.Diagnosis: The diagnosis of scurvy is usually clinical, particularly in infants, based on symptoms, a history of vitamin C deficiency and low blood levels of ascorbic acid.Treatment: Vitamin C administered by mouth or injection is effective for curing scurvy. If vitamin C is not available, orange juice can 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.
A
Common cold prevention (extreme environments)

Scientific studies generally suggest that vitamin C does not prevent the onset of cold symptoms. However, in a subset of studies in people living in extreme circumstances, including soldiers in sub-arctic exercises, skiers, and marathon runners, significant reductions in the risk of developing colds by approximately 50% have been reported. This area merits additional study, and may be of particular interest to elite athletes or military personnel.
B
Iron absorption enhancement

Based on scientific research, vitamin C appears to improve oral absorption of iron. Concurrent vitamin C may aid in the absorption of iron dietary supplements.
B
Alkaptonuria

Alkaptonuria is a disorder characterized by the absence of the enzyme homogentisic acid oxidase, with a resulting accumulation of homogentisic acid in the blood and urine. Limited research reports that daily high-dose vitamin C may provide symptomatic relief and slow progression of complications of this disorder. Additional evidence is merited in this area.
C
Asthma

It has been suggested that low levels of vitamin C (or other antioxidants) may increase the risk of developing asthma. The use of vitamin C for asthma has been studied since the 1980s (particularly exercise-induced asthma), although the evidence in this area remains inconclusive. Additional research is necessary before a clear conclusion can be drawn.
C
Cancer prevention

Dietary intake of fruits and vegetables high in vitamin C has been associated with a reduced risk of various types of cancer in population studies (particularly cancers of the mouth, esophagus, stomach, colon, or lung). However, it is not clear that it is specifically the vitamin C in these foods that is beneficial, and vitamin C supplements have not been found to be associated with this protective effect. Experts have recommended increasing dietary consumption of fruits and vegetables high in vitamin C, such as apples, asparagus, berries, broccoli, cabbage, melon (cantaloupe, honeydew, watermelon), cauliflower, citrus fruits (lemons, oranges), fortified breads/grains/cereal, kale, kiwi, potatoes, spinach, and tomatoes.
C
Cancer treatment

Vitamin C has a long history of adjunctive use in cancer therapy, and although there have not been any definitive studies using intravenous (or oral) vitamin C, there is evidence that it has benefit in some cases. More well-designed studies are needed before a firm recommendation can be made.
C
Plaque/ calculus on teeth



In preliminary study, a reduced amount of calculus, visible plaque and bleeding gum sites was observed after use of vitamin C chewing gum. Further research is needed to confirm these results
C
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. Although some study results show that daily supplementation can effectively lessen the incidence of premature rupture of chorioamniotic membranes (PROM). A gynecologist and pharmacist should be consulted before taking any herbs or supplements.
C
Stroke prevention

There are variable results of studies that have measured the association of vitamin C intake and risk of stroke. Some studies have reported no benefits, while other research reports that daily low-dose vitamin C may reduce the risk of death from stroke. Additional research is merited in this area. Individuals at risk of having a stroke should speak with their healthcare provider about the role of vitamin C supplements in stroke prevention.
C
Vaginitis

Preliminary human study shows that vitamin C vaginal tablets given once a day may help patients suffering from non-specific vaginitis. Further research is needed to confirm these findings.
C
Cataracts (prevention/progression)

Although population research initially suggested a reduction in cataract formation among individuals taking vitamin C for at least 10 years, subsequent prospective research found no reduction in the seven-year risk of age-related cataract formation or progression with the use of daily vitamin C.
D
Common cold prevention (general)

More than 30 clinical trials including more than 10,000 participants have examined the effects of taking daily vitamin C on cold prevention. 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 severity of symptoms has been seen overall, although a very small significant reduction in the duration of colds has been reported (approximately 10% in adults and 15% in children). Laboratory experiments in which volunteers are infected with respiratory viruses while taking vitamin C have yielded differing results, but overall report small or no significant differences in symptom severity following infection.Notably, a subset of studies in people living in extreme circumstances, including soldiers in sub-arctic exercises, skiers, and marathon runners, have reported a significant reduction in the risk of developing a cold of approximately 50%. This area merits additional study, and may be of particular interest to elite athletes or military personnel.
D
Common cold treatment

Numerous studies have examined the effects of starting vitamin C after the onset of cold symptoms. Overall, no significant benefits have been observed. Initial evidence from one study reports possible benefits with high doses of vitamin C taken at the onset of symptoms, but without additional evidence this remains indeterminate. At this time, the scientific evidence does not support this use of vitamin C.
D
Heart disease prevention



Vitamin C does not appear to lower cholesterol levels or reduce the risk of heart attacks. Effects on cholesterol plaques in heart arteries (atherosclerosis) remain unclear, and some studies suggest possible beneficial vasodilation (artery opening) properties. Based on the current scientific evidence, vitamin C is generally not recommended for this use. People at risk of heart attacks should speak with their healthcare provider to consider preventive measures such as aspirin.
D
Premature infants



In a randomized controlled trial, no significant benefits or harmful effects were associated with ascorbic acid supplementation throughout the first 28 days of life.
D


*Key to grades

A: Strong scientific evidence for this use;

B: Good scientific evidence for this use;

C: Unclear scientific evidence for this use;

D: Fair scientific evidence against this use;

F: Strong scientific evidence against this use.


Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.


Acne, Alzheimer's disease, anemia, anemia in hemodialysis patients, antiviral, antioxidant, atherosclerosis, attention deficit hyperactivity disorder, autism, bronchitis, capillary fragility, cervical dysplasia, Chediak-Higaski syndrome, constipation, cystic fibrosis, delayed onset muscle soreness, dental cavities, dermatitis, diabetes, eye disorders, fluorosis, furunculosis, gallbladder disease, gastric ulcer, hay fever,Helicobacter pyloriinfection, high blood pressure, high cholesterol, histamine detoxification, idiopathic thrombocytopenic purpura, immune stimulation, infertility, jellyfish stings, lead toxicity, male infertility, macular degeneration, melasma, menorrhagia, heavy metal/lead toxicity (mercury elimination), nitroglycerin activity prolongation (nitrate tolerance prevention), oligoasthenozoospermia, osteoporosis, pneumonia prevention, pressure sores, preterm labor, reduction of levodopa side effects, reflex sympathetic dystrophy, skin conditions (wrinkles), skin sun damage, stomach ulcers, sunburn prevention, tuberculosis, urinary acidification, wound healing.

Dosing

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 (18 years and older):

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 milligrams per day; for women older than 18 years-old is 75 milligrams per day; for pregnant women older than 18 years-old is 85 milligrams per day; for breastfeeding women older than 18 years-old is 120 milligrams per 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 milligrams per day has been recommended by some.


Upper limit of intake (UL) should not exceed 2,000 milligrams per day in men or women older 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 replete body vitamin C stores. Some experts have recommended 1-2 grams per day for two days followed by 500 milligrams per day 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.


Children (younger than 18 years):

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


Tolerable Upper Intake Levels (UL) have 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 milligrams per day; the UL for ages 4-8 years-old is 650 milligrams per day; the UL for ages 9-13 years-old is 1,200 milligrams per day; the UL for ages 14-18 years-old is 1,000 milligrams per day (including pregnant or breastfeeding females).

For scurvy/deficiency in children, 100-300 milligrams per day 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 asymptomatic vitamin C deficiency, lower daily doses may be used.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. 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.

Side Effects and Warnings
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 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. 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.

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.

Pregnancy and Breastfeeding

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 extra vitamin C throughout their 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 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

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. 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.


Interactions with Drugs

Vitamin C may increase adverse effects associated with acetaminophen.

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

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

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

Vitamin C supplementation may decrease levels of the drug fluphenazine in the body.

Concomitant administration of high doses of vitamin C can reduce steady-state indinavir plasma concentrations.

There is limited case report evidence that high dose vitamin C may reduce side effects of levodopa therapy such as nausea or malcoordination.

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

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

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

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

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.

Vitamin C may increase absorption of lutein vitamin supplements.

Large doses of vitamin C may interfere with the absorption and metabolism of vitamin B12.

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