C Vitamins

VITAMIN C (ASCORBIC ACID)

Despite the long history of experience and research with vitamin C, dating back several centuries to the search for the cause of scurvy among sailors on long voyages, we still have much to learn about how it works in the human body. We know that humans are one of the few creatures on earth that don’t make their own vitamin C, but we don’t know why.

Professor Linus Pauling proposed that humans’ inability to make ascorbic acid and the decrease in C content of our diet over the years, particularly as early humans shifted from an allvegetarian diet to a partly meat diet, has placed us at risk for getting less vitamin C than we need for optimum health. Some vitamin C advocates are quick to point out that animals that make their own vitamin C produce the human equivalent of 10 to 20 g per day. The average human diet, on the other hand, contains only 30 mg per day. They also point to apes, which get an average of 5 g of vitamin C a day in the wild.

This theory is disputed by many nutritional experts, who claim that humans’ diet was probably never strictly vegetarian and has always contained both meat and vegetables. Conventional wisdom tells us that if the ability to make vitamin C had been needed in our species’ early history, it would have been carried down to today’s humans through our genes. Some evidence indicates that animals make their own vitamin C in large amounts because they use it up much faster than we do. Perhaps humans are more efficient than most members of the animal kingdom in that we efficiently absorb and can store small amounts of vitamin C. Why carry the machinery to make vitamin C when you can let plants do it for you? Both sides of this debate are pure speculation, and no one can conclusively prove any of these points. Nevertheless, as knowledge of the importance of antioxidants in the diet grows, increasing vitamin C intake seems like a good idea (see Chapter 7).

FUNCTION

Vitamin C is a modified sugar molecule that is water soluble. One of the important functions of vitamin C is to serve as a water-soluble antioxidant and free-radical scavenger (see Chapter 7). It is one of the compounds in the body that protects us from oxidative free-radical damage.

It is also known that vitamin C is necessary in the synthesis of hydroxyproline and hydroxylysine. These hydroxylated amino acids are building blocks of collagen, the main supporting component in connective tissue, which is the tissue that holds us together. Some types of connective tissue are cartilage, tendons, and fibers. A lack of vitamin C causes defects in the formation of mucous membranes and interferes with the normal healing of wounds. Without sufficient vitamin C, the tissue that surrounds and supports capillaries (the smallest blood vessels) breaks down, and the capillaries themselves then break from lack of support. This results in black-and-blue bruise marks as blood leaks into tissue and clots there. The hallmark of scurvy, the vitamin C deficiency disease, is a lack of collagen synthesis.

Vitamin C also stimulates the adrenal glands to manufacture cortisone and other body hormones involved in helping us cope with stresses of daily life. Vitamin C levels are high in the adrenal glands. Vitamin C is known to participate in the hydroxylation of a chemical called dopamine in the adrenal gland to form the neurotransmitter norepinephrine. Norepinephrine is essential to life because it affects many parts of the central nervous system and all of our major organs. Another important chemical in the body whose synthesis is dependent on vitamin C is carnitine. Carnitine is needed to move sugars into the mitochondria of the cells so that they can be metabolized to yield energy.

Vitamin C increases the amount of iron absorbed from non-meat sources through the intestines by chemically reducing and chelating the iron. To be effective, the vitamin C must be taken at the same time as the iron. If you have iron-deficiency anemia, taking the iron tablet simultaneously with 100 to 200 mg of vitamin C will increase absorption by 30 to 40 percent. The vitamin C is involved in the conversion of folic acid to its active form, dihydrofolic acid, in the body. In fact, one of the features of vitamin C deficiency is an anemia similar to the kind found in people deficient in folic acid. Small amounts of ascorbic acid are also needed to break down cholesterol in the blood.

White blood cells contain relatively large amounts of vitamin C, and it seems to be key to the ability of these cells to attack and engulf invading bacteria. Immune function is diminished in vitamin C deficiency. Deficient individuals are more susceptible to viral and bacterial infections. Interferon production by cells is stimulated by vitamin C, which may account for its importance in the defense against viruses. In addition, vitamin C is involved in the manufacture of a group of enzymes that are essential to the body’s ability to break down drugs and other chemicals the body considers foreign.

DAILY REQUIREMENTS

Only about 10 mg a day of ascorbic acid is enough to protect against scurvy, which is the disease resulting from a deficiency of vitamin C. Nevertheless, the average adult RDA for ascorbic acid has been set at 60 mg to provide an extra margin of safety during times of illness and stress. In the United States it is estimated that 20 to 30 percent of adults consume less than the RDA value. A current controversy is whether levels of vitamin C over the RDA value are needed for optimal health. Given the importance of this vitamin as a water-soluble antioxidant we believe that higher levels would be beneficial (see Chapter 7). In considering what intakes might be optimal, it is important to note that 200 mg will provide about 80 percent of complete saturation of blood. Because vitamin C is “pumped” into cells by an enzymatic process, blood cells and body tissues are completely saturated at this dose. Doses of 500 mg to 1,000 mg will saturate blood. Vitamin C intakes of RDA amounts (30 mg–90 mg) will not saturate. Thus if you believe that for optimum health, you want to saturate your body with vitamin C, you will need to take in more than 200 mg per day. If five portions of fruits and vegetables were consumed each day, as recommended by nutrition authorities, vitamin C intake would be in the 100 to 300 mg per day range. Researchers at the National Institutes of Health note that 100 mg to 200 mg of vitamin C daily will benefit most healthy Americans. Intakes higher than 300 mg will be difficult to achieve without taking supplements.

DIETARY SOURCES

Fruits, potatoes, and green vegetables are the best natural sources of this vitamin. There is little vitamin C in meats, cereals, grains, and the foods we normally think of as being loaded with B vitamins. Interestingly, the richest sources of vitamin C are not the citrus fruits, as we have been led to believe, but rose hips, broccoli, Brussels sprouts, and green peppers. Additional good sources are listed in the accompanying table.

Vitamin C is chemically unstable and therefore presents some problems in terms of storage and processing. Drying fruits and vegetables destroys much of their vitamin C content. In one experiment, up to 54 percent of the vitamin was destroyed by drying. Vitamin C also breaks down after exposure to light and air. In addition, long storage of fruits and vegetables allows the vitamin to be broken down by natural enzymes. Another problem unique to ascorbic acid is that if fruits and vegetables are picked before they reach their fully ripened state, they will not have produced their full quota of vitamin C.

Freezing does not destroy the vitamin C content of foods. A typical cup of freshly squeezed orange juice contains 100 mg of ascorbic acid, while a cup of juice reconstituted from frozen concentrate contains about 120 mg of the vitamin, probably because of a special effort to concentrate ascorbic acid during the quick freezing process and the fact that vitamin C is most stable in an acid medium, such as fruit juice. However, the vitamin in frozen orange juice can be broken down by oxygen as soon as the juice is reconstituted and warmed to refrigeration temperatures.

VITAMIN C (ASCORBIC ACID) CONTENT OF SELECTED FOODS
(Average adult RDA is 60 mg)

Estimates of actual cooking losses range between 30 and 60 percent, although some procedures, such as blanching vegetables and then cooking them in iron or copper pots, can result in the destruction of almost all of the vitamin C. In summary, the vitamin C content of foods is highly variable. For optimal C content, consume fresh, uncooked fruits and vegetables and drink reconstituted frozen juices.

DEFICIENCIES

The disease associated with vitamin C deficiency is scurvy, which was common in sailors (who had little access to fresh foods during long voyages) in the days before vitamin C was known. Also hard hit were people in northern climates who did not have access to fresh fruits and vegetables during the long winter months. Now our ability to transport fresh food over great distances has dramatically decreased the amount of scurvy worldwide. Nevertheless, marginal vitamin C deficiencies still exist in some people, even in Westernized countries. It takes several months of a vitamin-C-deficient diet before scurvy develops. However, marginal deficiencies can develop sooner.

Deficiency Symptoms

Our basic descriptions of the symptoms of scurvy come from the logs Jacques Cartier kept during long sea voyages. Cartier’s log, written in 1535, graphically tells how severe the disease can be: “Unknown sickness began to spread itself amongst us at the strangest sort that was ever heard or seen; inasmuch that some did lose all their strength and could not stand upon their feet; then did their legs swell, their sinews shrunk and became black as coal. Others also their skins spotted with spots of blood, of a purple colour. It ascended up their ankles, knees, thighs, shoulders, arms and neck. The mouth became stinking; their gums so rotten that the flesh came away to the roots of their teeth, which at last did fall out.” The latter symptom is a result of periodontal disease, which can be caused by vitamin C deficiency as well as other factors.

Some symptoms of marginal deficiency are fatigue, shortness of breath, digestive difficulties, bleeding gums, easy bruising, swollen or painful bone joints, nosebleeds, anemia (weakness, tiredness, loss of color), more frequent infections, and slow wound healing. Some nutrition experts claim that people deficient in C who are at risk for heart attacks or strokes are more likely to develop one of these serious problems because of blood vessel weakness.

Vitamin C can be measured directly in the blood. The symptoms of scurvy start to appear when the blood level falls below 1 mg for every 100 ml of blood. The vitamin can also be measured in white blood cells. These levels are often taken as a better representation of the amount of vitamin C in body tissues because they are not as subject to variation as the blood level.

PEOPLE WHO MAY BENEFIT FROM SUPPLEMENTATION

Senior Citizens

Marginal C deficiencies have been found in seniors, particularly those living in nursing homes or other health care facilities. The reasons for this deficiency seem to be inattention to diet, the loss of appetite, and in some cases difficulty digesting foods rich in vitamin C, many of which are also high in roughage. On the basis of this information, we suggest that all people over age sixty-five take a daily multivitamin containing at least 60 mg of ascorbic acid. Of course, this does not eliminate the need for a balanced diet, including vitamin C–rich foods, but it does provide a measure of protection against possible deficiencies.

Other Groups

Pregnant women should supplement their daily vitamin C intake because of the demands by the fetus’s developing bones, teeth, and connective tissue. Breast-feeding women also need supplemental C because they must supply enough vitamin C in their milk to support their baby’s rapid growth. Smokers, women who take oral contraceptives, and people under any kind of stress (including those with infections or other medical illness or injury, those undergoing surgery, or those experiencing psychological stress) should supplement their daily intake of vitamin C, but the amount does not have to exceed 500 mg per day.

TOXICITY

Vitamin C is considered nontoxic in doses less than 1 g per day. Over 1 g, less is known about long-term consumption. However, large-scale clinical trials involving thousands of volunteers who received between 1 and 30 g of vitamin C per day revealed very few problems. Since the 1970s large doses of vitamin C have been consumed by millions in the United States with very few reports of adverse effects. As discussed later, the body is saturated at about 500 mg per day, and higher doses are simply eliminated in the urine.

There are scattered reports of a variety of adverse reactions to vitamin C, including upset stomach and diarrhea, but these are rare. Because vitamin C is metabolized in the body to oxalic acid, which is relatively insoluble in urine, high doses of C have the potential to contribute to the formation of kidney stones. High doses can also block the body’s ability to eliminate urate, which could be deposited in joints, causing gout. The significance of these risks is controversial, but if you have bladder problems, kidney stones, or gout, we suggest not using large (over 200 mg) amounts of vitamin C because of potential problems associated with crystal deposits.

Patients with iron overload conditions should avoid large amounts of vitamin C because it will increase iron absorption. Hemolysis (the bursting of red blood cells) has been reported in patients having glucose-6-phosphate dehydrogenase (G6PD) deficiency. This deficiency makes patients susceptible to hemolysis from taking many common drugs. These patients need to avoid high-dose vitamin C.

Sudden stoppages of large doses of vitamin C have been reported to result in deficiency symptoms. This is called rebound scurvy; it is considered a very rare event and is not well documented. This is also true of infants born of mothers who consumed megadoses of vitamin C. They have developed deficiency symptoms soon after birth, probably because their body tissues had become used to very large amounts of vitamin C in the blood circulating from their mother. High doses of any vitamin or mineral should be avoided during pregnancy because the risks are simply not known.

INTERACTIONS

Vitamin C can interfere with certain urine and blood tests for sugar and for the test for occult blood in the stool. See Part 6, “Vitamin, Mineral, and Herbal Drug Interactions.”

THERAPEUTIC USES

Vitamin C supplements may be given to counteract any of the standard symptoms of vitamin C deficiency reviewed earlier in this profile. However, such symptoms will not be alleviated by vitamin C unless they are, in fact, caused by vitamin deficiency.

Antioxidant Uses

The important role of vitamin C as a water-soluble antioxidant and free-radical scavenger is discussed in Chapter 7. Low dietary vitamin C intake has been associated with increased risk for cancer, especially cancer of the stomach, throat, intestines, and lungs. Low intake also increases the risk for heart disease, high blood pressure, and cataracts.

Wound Healing

Vitamin C is often given after surgery to speed the healing of surgical wounds. Vitamin C has an important role in the synthesis of new connective tissue, and controlled studies have shown that supplements speed up healing of bedsores and experimentally administered cuts in the mouth. Not all studies show benefit, however. We suggest that supplements be used following any significant injury or surgery in order to ensure ample vitamin C to help speed the healing process. Doses of 250 to 500 mg per day are sufficient for this effect.

UNSUBSTANTIATED CLAIMS

Prevention and Cure of the Common Cold

The claim that vitamin C will cure or prevent the common cold is of obvious interest to everyone. This is not a new idea, but it was popularized in 1970 with the publication of Vitamin C and the Common Cold, by Dr. Linus Pauling. Incredibly, surveys have shown that as many as half the American people have, at some time, taken extra vitamin C to prevent or treat the common cold, an illness responsible for billions of dollars’ worth of lost time and productivity each year. Advocates of this treatment claim that between 1 and 5 g a day of ascorbic acid will prevent the common cold and that still higher doses are useful in treating cold symptoms, if you are unlucky enough to get sick in spite of the prevention regimen.

What is the evidence? Vitamin C advocates usually cite the results of studies conducted in the 1940s and 1950s, but most of these early studies are technically incorrect and have been criticized for that reason. The publication of Linus Pauling’s book and the increased popularity of vitamin C have sparked careful evaluations by a number of reputable investigators. At least ten careful, technically correct studies have appeared in the literature since 1970. What emerges from these investigations is a picture far less optimistic than that presented by advocates. In these large, controlled studies, Vitamin C does not seem to have much of an effect in preventing the cold but has a small effect in decreasing its severity.

One study worth noting was conducted using school-age twins as subjects. One twin from each pair was given vitamin C (adjusted for age, but in the range suggested by advocates), while the other was given a placebo with the same appearance and taste of the vitamin C. As the twins lived in the same household, they were exposed to all the same factors, such as diet and contact with others, that could potentially influence a cold. Technically, this was a nearly ideal experiment. The results of this study were similar to those reported by other investigators: The children taking vitamin C had somewhat less severe colds, but the number of colds was essentially the same as experienced by those taking the placebo.

Despite the evidence from the large clinical trials, many claim to benefit from taking vitamin C during the winter months. Probably everyone has friends and coworkers who swear by vitamin C and claim, “I never get a cold while I take vitamin C.” It is difficult to evaluate these claims of success. The evidence shows otherwise. There may be a subset of the population that strongly benefits, but their response does not show up in the large trials. On the basis of the evidence, you might expect a mild reduction in cold symptoms, although the high doses usually suggested do not seem to be necessary. Studies have been conducted in which a dose of between 80 and 200 mg per day was sufficient to produce this effect (a glass of orange juice contains 100 to 125 mg). It is possible that a small number of people are deficient in vitamin C or need unusually large amounts. Taking extra vitamin C will help these few people. We believe that a saturation-level dose of vitamin C (200 to 500 mg per day) is enough to provide excellent antioxidant and free-radical-scavenging activities and will optimize the immune system to fight infections such as the common cold.

Cancer

In the 1970s there was some enthusiasm for using very high doses of vitamin C in the treatment of cancer. Interest has waned, however, as the results from several trials did not show benefit. Now most attention is focused on the antioxidant properties of vitamin C and the connection between supplementation with antioxidants and protection against cancer. As discussed in Chapter 7, vitamin C is an important link in the antioxidant sequence, but vitamin E may be the most important antioxidant vitamin with respect to cancer and heart disease prevention. Consumption of fruits and vegetables high in vitamin C is protective, and this is the best step you can take to decrease risks. Additionally, we recommend daily consumption of 200 to 500 mg of vitamin C to optimize antioxidant and free-radical protection.

Detoxifying Alcoholics and Drug Abusers

There are a small number of unverified reports attesting to the usefulness of enormous doses of ascorbic acid, in some cases given by injection, in drying out alcoholics and detoxifying people addicted to narcotics and tranquilizers. People treated with vitamin C are given massive doses (up to 85 g a day) and are supposed to experience fewer of the adverse effects normally associated with drug withdrawal: cramps, nausea, generalized discomfort. This application of vitamin C should be considered unproven, although future research may shed some light on a possible role for this vitamin in this regard.

Cholesterol and Lipid Lowering

The story of vitamin C and blood lipids is riddled with conflicting information. While there is agreement that ascorbic acid will lower blood cholesterol in vitamin-deficient patients, it does not necessarily follow that cholesterol levels in other people will be affected. In fact, studies have shown that people with high blood cholesterol who are otherwise healthy are not affected by vitamin C. There are better drugs to lower cholesterol.

AVAILABILITY

A stroll down the vitamin aisle of your local pharmacy, health food, or vitamin store will soon make you aware that ascorbic acid is available in just about every possible dosage form (tablet, capsule, liquid, syrup, natural, synthetic, crystals, chewable, timed-release, wafers) and strengths (25 mg to 1,500 mg). The combination of vitamin C with bioflavonoids improves vitamin C absorption somewhat, but these products are more expensive, and at doses of over 500 mg per day, the small extra amount absorbed is probably not important. Timed-release products are poorly absorbed. Synthetic vitamin C tablets are fine and are inexpensive.