Vitamin C

Vitamin C (ascorbic acid or dehydroascorbic acid) is an essential water-soluble vitamin that the human body can't manufacture. It must, therefore, come from foods or supplements. Fruits and vegetables are the richest food sources of vitamin C. Dietary supplements are typically sold as ascorbic acid, calcium ascorbate (Ester-C®), sodium ascorbate, or a combination of these forms. Supplements also commonly contain natural sources of vitamin C such as rose hips (the pear-shaped fruit of the rose, without the flower's petals) and/or acerola (a cherry-like fruit).

Vitamin C helps the body produce collagen, a basic component of connective tissue. Collagen is an important structural element in blood vessel walls, gums, and bones, making it particularly important to anyone recovering from wounds or surgery. Vitamin C also acts as an antioxidant, scavenging potentially harmful molecules called free radicals. Although not established by clinical trials, this antioxidant activity is theorized by some to help protect against cancer, cataracts, age-related macular degeneration of the retina, age-related skin changes and other chronic diseases. Vitamin C intake may be particularly helpful to smokers, who may suffer from oxidative stress and cell damage, which can deplete the body's store of vitamin C.

Vitamin C supplements may boost the immune system. Regular use of vitamin C can not prevent colds but may slightly reduce symptoms and the duration of a cold. An exception is that vitamin C can reduce the chance of getting a cold after endurance exercise, such as a marathon, when taken for a period of time prior to the event. It may also help maintain the effectiveness of nitrate drugs, such as nitroglycerin. Vitamin C can enhance iron absorption from supplements and plant foods.

What to Consider When Buying
Both natural and synthetic vitamin C are equally recognized and used by the body, so all-natural rose-hip or acerola products provide no added benefit if you just want vitamin C. In fact, some products stating "with rose hips" but not indicating the amount may contain far more synthetic vitamin C than vitamin C from rose hips. (Hint: A product's ingredient list gives a clue to the amount of rose hips present. Ingredients on that list must appear in the order of amount, from greatest to least. If rose hips appear last, there isn't much in the product.)

Ester-C® (calcium ascorbate) is a non-acidic form of vitamin C that may be beneficial for people who experience symptoms of acid stomach from ordinary vitamin C. Note, however, that diarrhea associated with higher intakes of vitamin C has nothing to do with acidity. Ester-C® also claims to be better absorbed than regular ascorbic acid, but this claim has not yet been supported by reliable evidence. Sodium ascorbate is also non-acidic. Products containing sodium ascorbate combined with ascorbic acid offer reduced acidity and are sometimes called "buffered vitamin C." Slow-release products may also help reduce digestive problems occurring with very high doses.

Some products claim "L-ascorbic acid" — it is just another name for vitamin C.

What to Consider When Using
When looking for a dosage, be aware that 1,000 mcg (micrograms) equals 1 mg (milligram), and 1,000 mg equals 1 gram. The RDA (Recommended Dietary Intake) is 90 mg/day for adult males and 75 mg/day for adult females. An additional 35 mg/day is recommended for smokers. For pregnant women ages 18 and younger, the RDA is 80 mg/day and for pregnant women older than age 18, it's 85 mg/day. For breast-feeding women ages 18 years and younger, the RDA is 115 mg/day and for breast-feeding women older than age 18, it's 120 mg/day.

The RDAs for children are as follows: 15 mg/day for children ages 1 to 3, 25 mg/day for children ages 4 to 8, and 45 mg/day for children ages 9 to 13. For males ages 14 to 18, the RDA is 75 mg/day. For females ages 14 to 18, it's 65 mg/day.

The RDAs are achievable with healthful diets and are also more than adequate for normal collagen production. However, some healthcare professionals recommend higher daily doses of vitamin C, such as 500 to 1,500 mg/day for adults, claiming that such doses stimulate the immune system and help prevent some chronic diseases.

Vitamin C is safe when taken in moderate amounts, but be aware that too much vitamin C can cause diarrhea and other gastric disturbances. The Upper Tolerable Intake Level (UL) (a dose likely to be safe for the vast majority of healthy people) for vitamin C in adults is 2,000 milligrams/day. For children, the upper level for tolerable intake is 400 mg/day for children ages 1 to 3, 650 mg/day for children ages 4 to 8, 1,200 mg/day for children ages 9 to 13, 1,800 mg/day for teens ages 14 to 18 ages 14 to 18, and 2,000 mg/day for individuals 19 years and older. Individuals are generally advised not to exceed these levels unless under medical supervision.

The amount of vitamin C that may be helpful reducing the symptoms and duration of a cold if taken routinely during cold season is, in adults, 1,000 mg. A similar dosage is used to help prevent colds when taken for a period of weeks prior to an endurance event. See the Encyclopedia article on this site for the dose of vitamin C used for other conditions.

Concerns and Cautions:

• Concerns have been raised that long-term vitamin C treatment may increase the risk of kidney stones. However, evidence from large epidemiological studies indicate that people who regularly consume large amounts of vitamin C either experience no increased rate of kidney stone formation, or actual protection from kidney stones. However, case reports suggest that certain individuals may be at increased risk for developing kidney stones if they take vitamin C supplements. For this reason, people with a history of kidney stones, or those with known defects in metabolism of oxalate or vitamin C, might be best advised to limit vitamin C intake to RDA levels.
• One study has suggested that vitamin C might reduce the effectiveness of statin-type cholesterol lowering drugs — however this has not been conclusively demonstrated.
• Another study suggests that high dose vitamin C might reduce the effectiveness of the HIV drug indinavir.
• Vitamin C may also interfere with the absorption of tricyclic antidepressants and anticoagulants.
• Excess vitamin C from supplements can interfere with diagnostic tests for cholesterol, blood sugar levels, and for blood in the stool.
• The risk of liver damage from high doses of acetaminophen (Tylenol®) may be increased if you also take large doses (3 grams) of vitamin C.
• Because vitamin C improves iron absorption, people with diseases that cause them to store too much iron should use vitamin C only with caution.
• There is test-tube evidence that vitamin C can cause the production of DNA-damaging genotoxins that may promote the development of cancer — arguing against high dose vitamin C as a way to reduce cancer risk.
• One study found that taking vitamin C along with Pycnogenol (an extract of pine bark, also known as OPCs or oligomeric proanthocyanidins) might raise blood pressure levels in people with hypertension. The reasons for this unexpected finding are currently unclear.