Vitamin C - Ascorbic Acid

• Method of Action
• Consequences of Deficiency
• Deficiency Symptoms
• Recommended Dietary Allowances

• Properties and Uses
• Toxicity Levels
• Food Sources
• Buffered Vitamin C

Description

Vitamin C (Ascorbic Acid) is a water soluble, white crystalline material that is stable in dry form. Much ascorbic acid is lost in cooking, but the loss can be reduced by cooking quickly in small amounts of water, or steaming foods with the pot covered tightly. Preservation is also accomplished via quick freezing.

Vitamin C has many functions: it can function as a coenzyme or as a cofactor in the body. It appears to be necessary for the normal function of cellular units and subcellular structures. In metabolism, vitamin C functions to accept and donate hydrogen. Vitamin C also plays an important role in the synthesis of neurotransmitters, compounds which allow nerve impulse transmission between nerve axons.

Production of collagen, a protein substance in fibrous tissue, depends on ascorbic acid. Vitamin C maintains capillary integrity through the production of an intercellular cement substance. This function promotes the healing of wounds, fractures, bruises, some hemorrhages, and bleeding gums. Additionally, it reduces susceptibility to infections.

Vitamin C helps to facilitate the absorption of iron and calcium, and it is essential for the utilization of folacin.

Method of Action

Humans absorb vitamin C in the upper part of the intestine. This is accomplished by simple diffusion, a sodium-dependent active transport mechanism. When megadoses are taken (1.5 to 3.0 grams) the absorption is only 36 to 49%. At intakes of 12 grams, only 16% is absorbed. Unabsorbed vitamin C continues into the lower bowel and causes watery stools or diarrhea.

Intakes of vitamin C above 100 mg do not result in an increase of ascorbic acid levels. Immediately after ingesting vitamin C, the serum level is temporarily elevated. The level subsides when the excess is picked up by the tissues that store it, or is excreted. The highest concentration of stored vitamin C is in the adrenal gland; however, the liver stores the largest amount of the vitamin in the body.

Vitamin C is excreted in the urine after enough is resorbed in the kidneys to maintain a plasma level of 1.2 to 1.4 milligrams per 100 milliliters.

Vitamin C plays a vital role in the formation of collagen by catalyzing chemical changes that allow lysine and proline to bind together as collagen subunits, adding structural stability to the "complete" collagen fibers.

Vitamin C is important and necessary for the synthesis of the neurotransmitters, norepinephrine and serotonin. It catalyzes the conversion of dopamine to norepinephrine and the conversion of tryptophan to serotonin.

Properties and Uses

Vitamin C has recently been the subject of controversy. Popular literature suggests that large doses (one gram or more) may prevent or cure the common cold or influenza. Scientists are presently conducting studies to establish the validity of this claim.

One study demonstrated that vitamin C reduced the severity of cold symptoms. A subsequent study indicated that the result of decreasing symptoms was the result of an increased dosage at the onset of illness and was not due to an increased daily dosage during non-illness. Contradictory findings in a study of children indicated a decreased severity of symptoms with the administration of one to two grams per day. It is important to note that these contradictory results may be due to differences in the vitamin C status at the beginning of the studies.

Vitamin C supplementation is beneficial for patients suffering from scurvy and its symptoms. Recommended dosages for these patients are 100 mg three times per day, with the alleviation of symptoms usually apparent in five days.

Consequences of Deficiency

Vitamin C deficiency is not common. Populations subject to vitamin C deficiency are alcoholics, people who consume a diet devoid of fruits and vegetables, elderly individuals on a limited diet, severely ill individuals under chronic stress, and infants fed exclusively cow's milk.

Deficiency symptoms may appear the first month following deprivation, when the serum level has been reduced to 0.2 mg/dl. Scurvy is caused by severe vitamin C deficiency, with symptoms including: anemia, weakness, poor appetite and growth, tenderness to touch, swollen and inflamed gums, loosened teeth, swollen wrist and ankle joints, and shortness of breath. Furthermore it may be observed that wounds fail to heal or previous wounds break down, and that infections develop easily in bleeding areas of the gum and skin. These effects are attributed to problems with collagen formation. It is also hypothesized that vitamin C is involved in the blood clotting mechanism.

Psychiatric symptoms of vitamin C deficiency include depression, hysteria, and hypochondriacal symptoms.

Smoking acts as an antagonist to vitamin C. Less vitamin C is available in smokers for utilization and storage, and smokers need twice the amount of vitamin C as the nonsmoker to show a comparable blood level.

Toxicity Levels

Massive doses of vitamin C have been implicated in "rebound scurvy," when the conditions occurs after the cessation of administration of these massive doses. It has been hypothesized that this is due to a high rate of vitamin C catabolism as an adaptation to hypersaturation. After reducing the vitamin C intake, the catabolism does not return to normal levels and this produces a vitamin C deficiency state.

Excess vitamin C excreted in the urine produces a false positive test for glucose. Excess vitamin C has also been implicated in the formation of orate and oxalate stones. However, current evidence suggests that large doses (nine grams per day) produce only a small increase in urinary oxalate.

Recommended Dietary Allowances

• RDA for adult males: 60 mg
• RDA for adult females: 60 mg
• RDA for children 7 to 10 years: 45 mg
• RDA for infants: 35 mg
• RDA for pregnant and lactating women: 95 mg

The Nobel prize winners: Albert Szent Georgi and Linus Pauling, both of whom spent many years researching this vitamin, recommend a daily intake of at least 2 grams, and have seen no toxic side effects at much higher doses, with many benefits. Any writings on the subject by either man is very much worth reading and consideration.

Food Sources

Summary Deficiency Symptoms