If you are concerned about your iron intake, consider some of these sources:

* Lean meats and shellfish

* Whole grain or enriched cereals

* Dried apricots, prunes, or raisins

* Nuts and wheat germ

* Dried beans and peas

* Leafy green vegetables

Liver, especially pork liver, contains large amounts of iron. But it is also rich in cholesterol. Too many of us eat too much of cholesterol-containing foods. Egg yolk has a moderate iron content; it is high in cholesterol, too.

The iron in flesh foods, called heme iron, is best absorbed by the body. Yet studies have found no more iron-deficiency anemia among vegetarians than among meat eaters.

One possible explanation is vitamin C. It enhances absorption of the iron in foods. Vegetarians often consume more vitamin C than meat-eaters. The vitamin C may compensate for the absence of meat in their diets.

A Look at Lead

Lead has long been in the headlines. Lead poisoning has occurred too frequently among children – often from eating chips of old paint that contained lead.

Whatever lead also plays any role in the cancer process is an open question. Only a few studies have been done – mostly in animals. These studies suggest that large amounts of lead might increase the risk of kidney cancer. But this form of cancer is not very common. (I never forget my friend, a medical doctor, who died 4 years ago, at the age of 40, due to kidney cancer).

The committee on Diet, Nutrition, and Cancer declined to make any recommendations regarding lead.

Some Advice about Canned Foods

Lead remains a concern to health experts for other reasons. The chances of getting lead poisoning are not great, but the problems has yet to be eliminated in U.S. and other countries. Infants, children, and pregnant women are at greatest risk.

Scientists estimate that food accounts for 55 – 85 percent of our exposure to lead. The lead in canned foods can seep into the food itself. Public pressure and encouragement from the Food and Drug Administration (FDA) have led canners to reduce the lead content of food by almost 40 percent during the last 30 years.

Acidic foods packed in cans made with lead are the most likely to absorb this mineral. Fruits and fruit juices, including tomato products, fall into this category. If these foods are stored in the can after opening, the lead content can increase fivefold in less than a week.

Lead experts urge us not to store acidic foods in cans after opening. Transfer the food to a glass or plastic container. This precaution will go a long way to preventing unnecessary lead in the diet. Foods taste better, too, when this advice is followed.

Unfortunately, there is no easy way to tell whether a csn has been soldered with lead. Evaporated milk is usually packed in lead-soldered cans. Infant formulas are not. Processed meats are also usually packed in non-leaded cans.

There’s Much More to the Story

Though research has yet to find that lead or other minerals play a major role in cancer prevention, the story of nutrition and cancer is not yet over. We have looked at vitamins, minerals, fiber, and cancer inhibitors. but there’s more to come.

The Next story tells about the dietary change that may offer the biggest dividends of all.

If you are nutrition-minded, you probably try not to lose nutrients in cooking.

With vitamin A, you don’t have to worry. It is tough stuff; pretty much indifferent to water, heat, and even long periods of storage. Vitamin A doesn’t dissolve in water, so it doesn’t leach into water used in cooking.

But vitamin C is very sensitive. Heat, light, and oxygen can do it in. In fact, some loss of the vitamin C in food just cannot be prevented.

With a little effort, though, losses of the vitamin can be kept to a minimum. Here are the rules:

1. The sooner fresh foods can be used, the better. Vitamin C breaks down during storage.
2. Try not to chop these foods finely all the time. The fewer pieces a food is cut into, the lower its exposure to oxygen, which destroys vitamin C.
3. The vitamin C in cabbage, cantaloupe, squashes, and strawberries is especially unstable. The sooner they are eaten after cutting, the better.
4. When using water to cook foods rich in vitamin C, boil the water first. Then add the food and cover the pot tightly. This cuts down on the oxygen coming in contact with the food.
5. Cook vitamin C-containing foods in as little water as possible. The vitamin can leach into the cooking water. Steaming in a basket or pressure-cooking is better, because less liquid will come into contact with the food.
6. If you do cook these foods in water, use the cooking water to make a sauce or save it for stock. This way, you won’t pour vitamin C down the drain.
7. Keep cooking time to a minimum. The longer the food is cooked, the more vitamin C will lose.

It is not always possible, of course, to follow these rules, but when it is, do so. The vitamin will also hold up better if not heavily exposed to light.

About Frozen Foods

All of this talk about losing vitamin C must make you wonder if any of it is left in processed foods. The answer is: it depends.

In some cases, the ability of the food industry to preserve the vitamin C in food is no less than amazing. In other instances, though,  it seems that processors are not trying hard enough.

My favorite example is frozen orange juice concentrate. It contains hardly a milligram less vitamin C than the oranges that it hails from. The juice processors have perfected their trade so well that it is almost an art.

Many other frozen foods do lose some vitamin C during the trip from field to supermarket. But their fresh counterparts are likely to do so, too, during storage and cooking. So, though fresh, raw vegetables usually have the most vitamin C, once cooked, their C content may be on a par with that of frozen foods.

If you observe the rules on preserving the vitamin C in foods, your fresh, cooked vegetables may retain more vitamin C than frozen ones.

Is There Vitamin C in That Can?

For canned fruits and vegetables, the story is not so good. Canned foods often have less vitamin C than frozen or fresh foods. The vitamin C leaches into the water used in packing.

So even though a canned food might have a lower cost per pound than the fresh or frozen version of the same item, it is not necessarily the best buy. If the canned version has only half as much vitamin C as the frozen, for instance, it actually can cost more to get 20 mg of vitamin C from it.

I do not want to imply that canned foods have no nutritional value. Nor do I mean to say that canned foods should never be used. But nutritionally, frozen foods are often a better buy. When in season, fresh foods are often a better buy, too. And fresh or frozen foods usually have less salt – a big plus.

You almost always can depend on fresh, uncooked foods for vitamin C (provided that the food is a source of the vitamin). When you eat fresh, raw foods, you don’t have to give a thought to losses that occur during cooking.

Remember: the vitamin C that remains in frozen or fresh foods can be destroyed by too much exposure to heat, light, and large amounts of cooking liquid. But a little effort can go a long way toward preventing unnecessary losses of this important vitamin.

I suggest you to find other valuable stories concerning vitamin C and cancer as follows:

• Vitamin C and Cancer
• Vitamin C, Cancer, and Kidney Stones
• Vitamin C, Cancer, and Kidney Stones, Part II, and
• Protect Yourself Against Cancer with your Daily Foods

The RDA for vitamin C is 60 mg a day for adults. By the way, 60 mg of pure vitamin C crystals would measure only a fraction of a teaspoon.

The scientists who set the RDA, however, did not take the evidence on vitamin C and cancer into account.

Here is some more specific advice. Nutritionists have always recommended four or more servings a day of fruits and vegetables. I think at least two, and preferably three, should be foods supplying moderate to high amounts of vitamin C. I try to eat a food rich in vitamin C at every meal.

It is not hard. I can hardly start the day without my orange juice. So that is my first suggestion. Grapefruit juice is also a fine choice.

Here are some other tips that work for me:

• Top cereal with sliced peaches, bananas, or other foods that are good sources of vitamin C.
• Eat salads often, using deep green lettuce, green pepper, and tomato as ingredients.
• Add sliced peaches to chicken salad.
• Serve luncheon salads inside of fresh green peppers.
• Serve fruit for dessert. If the family objects, make sweets that include fruit. It is simple enough to top cakes or ice milk with sliced bananas, berries, peaches, or other fruit.

If you are wondering what qualifies as a serving, here are some guidelines. For juices, three-fourths to one cup is one serving. “Juice” glasses usually hold three-fourths of a cup (6 ounces). Full-size glasses usually hold a full cup (8 ounces).

Nutritionists generally consider three-fourths of a cup of a vegetable as one serving. If that doesn’t mean much to you, take a look at half cup and quarter cup measures to get an idea of what three-fourths of a cup looks like.

For most fruits, such as oranges, bananas, or apples, one whole fruit is one serving. For large fruits such as grapefruit, half of one fruit is one serving. In the case of very large fruits, such as melons, you can consider one cup of the fruit, diced, as one serving.

Vitamin A and C Often Go Hand in Hand

If it seems that eating to prevent cancer is getting complicated, rest assured that it does not have to be.

When it comes to eating more of the fruits and vegetables rich in vitamin A and C, you can often get both nutrients from the same foods. There are quite a few foods that are good sources of both of these important nutrients.

You might call them the fruit and vegetable  all-stars. Here is the lineup:

1. Asparagus, broccoli, cantaloupe, sweet potatoes, and tomatoes are high in both vitamin A and C.
2. Brussels sprouts, green pepper, and peas are rich in vitamin C and also contain moderate amounts of vitamin A.
3. Apricots, mangoes, mixed vegetables, peaches, romaine lettuce, spinach, and winter squash have medium amounts of vitamin C and high levels of vitamin A.
4. Dark green leafy vegetables, such as kale, collards, and turnip and mustard greens are also rich in vitamin A, with moderate amounts of vitamin C.
5. Corn, green beans, and watermelon have moderate amounts of both vitamin A and C.

One nice aspect of vitamins and cancer is that many of these foods complement each other in cooking. You can mix apricot nectar with orange juice to give a not-too-sweet breakfast beverage. That way you start your day right, with both vitamin A and C.

By the way, I cannot resist pointing out that most of these foods rich in vitamin A and C are pleasantly low in calories, too.

( The Next Story )

But an update is in order. It is not that vitamin C does not do these things. Rather, it does more – much more.

It may very well help to prevent cancer, says the Committee on Diet, Nutrition, and Cancer (of the U.S.). The panel members were impressed enough with studies of vitamin C and Cancer to advise us to eat foods rich in vitamin C every day.

Scientists have found that cancers of the stomach and esophagus are less common among people who eat diets rich in vitamin C. In fact, year-round access to foods rich in vitamin C may be one explanation for the dramatic fall in stomach cancer rates in the case of the United States.

Stomach cancer was common in the United States at the turn of the 20th century, when some fruits and vegetables were available only seasonally. We now have year round access to these fruits and vegetables, and many are rich in vitamin C. And stomach cancer is no longer common. It does remain a major health problem in some parts of the world.

A few studies also tie vitamin C to lower risk of bladder and colon cancer. But there is not enough research yet to make a firm judgment about vitamin C’s  ability to protect against these two forms of cancer.

How Vitamin C Protects Us

We have a pretty good idea of how vitamin C works to prevent cancer. Substances in food called nitrites can turn into cancer-causing nitrosamines during cooking or digestion. Bacon, of course, has a particularly bad record;  nitrosamines have often been found in it after cooking.

Laboratory scientists know that nitrosamines can be created by letting certain chemicals come in contact with each other. yet when vitamin C is added to the chemical mixture that normally results in nitrosamines, fewer of them form. In some cases, vitamin C has completely blocked the formation of nitrosamines.

Can the same thing happen in our bodies? Studies around the globe suggest that the answer is yes.

In the U.S., a team of  researchers found that the chances of developing cancer of the esophagus went down as the amount of fruits and vegetables in the diet went up. Researchers also know that Americans and Western Europeans have fairly low rates of stomach cancer. These countries enjoy access to a variety of fruits and vegetables.

On the other hand, fruit and vegetable intake is low in some of the regions where stomach and esophageal cancer are rampant. Iranians living along the coast of the Caspian Sea, for instance, have alarming rates of esophageal cancer. Researchers sent to find out why noted that fruits and vegetables were almost absent from the diets of these people.

Another Role for Vitamin C

Scientists have known for decades that vitamin C can block the chemical reaction called oxidation. Oxidation is the process that causes food to become rancid. Substances that prevent oxidation are called antioxidants.

Until recently, no one realized that antioxidants might help protect against cancer. But they very well may. Scientists now believe that some chemicals cause cancer only if oxidized. By preventing oxidations, vitamin C may cut down on our exposure to cancer-causing chemicals.

The Recommendation and How to Meet It

“Eat fruits, vegetables…… daily, especially those high in vitamin C,” advises the Committee on Diet, Nutrition, and Cancer. This is going to be a popular recommendations. Almost everyone – from babies to adults – likes foods rich in vitamin C.

To follow the committee’s advice, take a look at the following chart. It rates foods as low, medium, or high in this vitamin.
How about animal foods? Animal foods are not listed because the supply less than 10 % of the vitamin C in our diet. Fruits and vegetables are the foods to depend on for this nutrient.

Vitamin C in Fruits and Vegetables

Adapted from the work of Committee on Diet, Nutrition, and Cancer, National Academy of Sciences, USA, 1989

( The Next Stories )

The cabbage family is not the only group of foods that has shown potential to block the cancer process. Other foods may also have this ability – and some may be even more potent than foods of the cabbage family.

But the evidence for these other foods is not as strong. Some foods have inhibited cancer in studies on animals, but studies with humans have yet to be done. Other foods have been studied in only one or two experiments – too few for judgment. This is why some health institution such as Committee on Diet, Nutrition, and Cancer limited its recommendations to the cabbage family.

Of the other foods that might also contain inhibitors, the evidence is best for citrus fruits. The beneficial effect of these foods has ranged from weak to potent in studies with animals.

As for other foods, the evidence is just beginning to come in. But for your information, I would like you to know some of the possibilities now under further study:

• Celery and spinach have shown slight but significant inhibiting ability.
• Soybeans and lima beans have also shown some potential.
• Grains and vegetable oils may contains a substance with moderate inhibiting power.
• Green coffee beans have shown a powerful inhibiting effect in early studies. But roasted and instant coffee have shown only a weak effect.

Remember: for some of these foods only several studies have been done. This is far too little work to justify changing your diet.

Some Unanswered Questions

Scientists are still a little cautious about the cancer inhibitors in food. They aren’t 100 percent convinced that these substances are only beneficial.

The Committee on Diet, Nutrition, and Cancer tells us that its matter of weighing the pluses and minuses. On the balance, the panel scientists agrees that the good points of the cabbage family vegetables outweigh the bad points.

What are the bad points? Mostly, they fall under the label of “uncertain effects.”

As noted earlier, inhibitors seem to activate an enzyme system that is thought to detoxify harmful chemicals. There is some concern that this very same enzyme system may also enhance the power of some chemicals. In other words, the enzyme system may have both good and bad effects.

Despite information on this subject is incomplete, still,  the scientists recommend that we eat citrus fruits, whole grains, and cabbage family vegetables. Obviously, the scientists think that the pluses here outweigh  the minuses.

But until this question is settled, it is best not to go all out with cabbage family vegetables. Eating them often – but not exclusively – is probably the best course of action. Including them in your diet once or twice a week is a cautious, moderate approach.

Putting It All Together

Up to this point, you have read a great deal about fruits, vegetables, and grains. It is fitting, I think, to take a broad look at these foods to see how they score when all protective factors are taken into account.

There are four factors to consider: vitamin A, vitamin C, insoluble fiber, and inhibitors. To take a simple approach to these four factors, I have devised a rating system.

I gave a food one point if it contains a moderate amount of vitamin A and two points for a high level. I used the same system for vitamin C and for insoluble fiber.

I then awarded two points to the four members of the cabbage family that appear to contain a cancer inhibitor other than vitamin A and C or fiber. I gave one point to the other foods that might have a cancer inhibitor.

The Top-Scoring Cancer-Blocking Foods

When all the points were tallied, broccoli and brussels sprouts topped the list.

They were followed by some vegetables that many people eat little of: collards, kale, kohlrabi, mustard greens, and rutabagas.

But in third place were some familiar faces: oranges, grapefruit, cabbage, cauliflower, lima beans, and spinach. Watercress also rated with this group.

Chances are that you like some of these foods. Pick the ones you like best, and continue to enjoy them.

If you do, then you should think again. Exciting new research shows that nature gives us weapons that can fight back. And these weapons are not in exotic places. They are in common foods.

The substances I am talking about are not considered nutrients, because their absence does not cause a deficiency disease. These substances are little-known food elements. Only a handful of research scientists are familiar with them.

Scientists call them inhibitors. In laboratory animals, these substances show an impressive ability to inhibit the cancer process.

How Cancer Inhibitors Work

A cancer agent, such as one found in cigarette smoke, might cause cancer in half of the animals that are exposed to it. But when an inhibitor is given along with the cancer-causing chemical, fewer animals will develop cancer. The inhibitor prevents the cancer-causing chemical from doing its damage.

Exactly how inhibitors work is not known. But the best theory right now has to do with an enzyme system in the body’s cells. It is called the mixed function oxidase system. Scientists believe that this enzyme system may actually have the power to strip dangerous chemicals of their harmful effects.

Cancer scientists have been curious about inhibitors for a very good reason. Human studies do support the notion that certain foods help to block the cancer process. Several studies have found that people who often eat foods thought to contain inhibitors have less chance of getting cancer.

The Organs That Benefit

For the most part, inhibitors are linked to protection against cancer of the digestive organs. Research ties these inhibitors most strongly to reduced rates of stomach and colon cancer.

Cancer inhibitors may help to explain why many people who are exposed to cancer agents never develop cancer. Think about it. Everyone has been exposed to cancer agents. They are in the air. Or in the water we drink. Or in the work place. And sometimes in our food.

Why, then, does cancer strike one in four – not four in four?

A good intake of cancer inhibitors may be part of the answer.

The Recommendation and How to Meet It

The Committee on Diet, Nutrition, and Cancer took a close look at research on cancer inhibitors. The committee made one recommendation after looking at these important findings.

The recommendation advises us to emphasize foods belonging to the cabbage family of vegetables. There is good evidence that these foods contain cancer inhibitors other than vitamins A and C.

The most common foods of the cabbage family are broccoli, cauliflower, brussels sprouts, and of course, cabbage. Research has linked these four vegetables to reduced risk of both stomach and colon cancer. A few studies also link these foods to lower risk of rectal cancer.

There are other foods in this family of vegetables. But it is not possible to say whether these other foods are also linked to lower risk of these cancers. It is reasonable to believe that these other foods are more likely than not to contain the same cancer-blocking substances. But only further research will give a firm answer.

The following chart lists all the foods belonging to this family.

The Whole Cabbage Family

A Family of Many Names

Scientists have some strange jargon for the foods of the cabbage family. The most technical name for this group of foods is the Brassica family. They also refer to these foods as “cruciferous” vegetables.

The inhibitors found in broccoli, brussels sprouts, cauliflower, and cabbage have been named indoles. Research on indoles is so recent that tables listing the indoles content of foods are nowhere to be found. So it is not possible to rank foods by their indole level. Also it is not known whether cooking and storage influence the indoles in these foods.

The best advice is to select the foods of this family that you like best and eat them often – perhaps once or twice a week. Remember that many of these foods offer other bonuses: vitamin A or C, a low fat and sodium count, and a modest amount of dietary fiber.

( next story: the Part II )

I would drink my orange juice and eat my green peppers even if  it weren’t  for research linking vitamin C to prevention of cancer.

Some of my reasons are the same ones that bolster the advice to eat more fruits and vegetables that supply carotene.  Like these plant foods rich in vitamin A, foods rich in vitamin C are also low in saturated fat and sodium.

What’s more, fruits and vegetables that contain vitamin C are cholesterol-free. And they provide small to moderate amounts of dietary fiber. Eaten in large amounts,  the fiber in these fruits and vegetables helps to lower blood cholesterol levels.

There is more. Vitamin C is rarely recognized for its role in iron absorption. Yet we have known for many years that vitamin C helps the body to absorb iron.

The extent of iron deficiency in the United State and most industry countries have been greatly exaggerated, I believe, but there are probably more people taking in too little iron than is the case for other nutrients.

Because the body absorbs only about 10 percent of the iron taken in, factors that increase iron absorption are just as important as iron-rich food. In fact, some scientists believe that increasing absorption of iron, rather than boosting iron intake, is the key to improving iron nutrition. They may be right on target.

At moderate levels – such as 50 to 100 mg – vitamin C has been found to improve iron absorption by as much as 50 percent. Higher doses may result in even higher absorption. But very few of us truly need such as assist.

Vitamin C helps the body absorb iron in foods that are eaten at the same meal. The vitamin C in breakfast foods, for example, has little or no effect on the iron in foods eaten at lunch or dinner.

For some people, however, this is not good news. A small number of people have a condition that causes them to retain too much iron, which accumulates in various organs, causing health problems. People who have this condition should consult their physicians for advice about diet.

I would love to tell you that vitamin C will also help protect you from heart disease. But I cannot, because I am not at all convinced by these claims.

I have looked carefully at evidence that vitamin C lowers blood cholesterol levels. But I found other studies in which vitamin C supplements appeared to have raised the cholesterol level. Some studies show no difference. I really do not hold out much hope for an effect here.

But what more can you want from vitamin C? It does not have to play a role in prevention of every disease in order to be taken seriously.

In my opinion, vitamin C is as important today as it was two centuries ago, when the mysterious disease  called scurvy threatened the lives of sailors who spent months without fresh fruits and vegetables. It is hard to disagree with the advice to make more room for this familiar vitamin in our diets.

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin. Unlike most mammals and other animals, humans do not have the ability to make their own vitamin C. Therefore, we must obtain vitamin C through our diet.

Function

Vitamin C is required for the synthesis of collagen, an important structural component of blood vessels, tendons, ligaments, and bone. Vitamin C also plays an important role in the synthesis of the neurotransmitter, norepinephrine. Neurotransmitters are critical to brain function and are known to affect mood. In addition, vitamin C is required for the synthesis of carnitine, a small molecule that is essential for the transport of fat into cellular organelles called mitochondria, where the fat is converted to energy (1). Research also suggests that vitamin C is involved in the metabolism of cholesterol to bile acids, which may have implications for blood cholesterol levels and the incidence of gallstones (2).

Vitamin C is also a highly effective antioxidant. Even in small amounts vitamin C can protect indispensable molecules in the body, such as proteins, lipids (fats), carbohydrates, and nucleic acids (DNA and RNA), from damage by free radicals and reactive oxygen species that can be generated during normal metabolism as well as through exposure to toxins and pollutants (e.g., cigarette smoke). Vitamin C may also be able to regenerate other antioxidants such as vitamin E (1). One recent study of cigarette smokers found that vitamin C regenerated vitamin E from its oxidized form (3).

Role in Immunity

Vitamin C affects several components of the human immune system; for example, vitamin C has been shown to stimulate both the production  and function  of leukocytes (white blood cells), especially neutrophils, lymphocytes, and phagocytes. Specific measures of functions stimulated by vitamin C include cellular motility,   chemotaxis , and phagocytosis.  Neutrophils, which attack foreign bacteria and viruses, seem to be the primary cell type stimulated by vitamin C, but lymphocytes and other phagocytes are also affected ). Additionally, several studies have shown that supplemental vitamin C increases serum levels of antibodies  and C1q complement proteins  guinea pigs, which—like humans—cannot synthesize vitamin C and hence depend on dietary vitamin C. However, some studies have reported no beneficial changes in leukocyte production or function with vitamin C treatment. Vitamin C may also protect the integrity of immune cells. Neutrophils, mononuclear phagocytes, and lymphocytes accumulate vitamin C  to high concentrations, which can protect these cell types from oxidative damage.  In response to invading microorganisms, phagocytic leukocytes release non-specific toxins, such as superoxide radicals, hypochlorous acid (“bleach”), and peroxynitrite; these reactive oxygen species kill pathogens and, in the process, can damage the leukocytes themselves. Vitamin C, through its antioxidant functions, has been shown to protect leukocytes from such effects of autooxidation. Phagocytic leukocytes also produce and release cytokines, including interferons, which have antiviral activity. Vitamin C has been shown to increase interferon levels in vitro.

It is widely thought by the general public that vitamin C boosts the function of the immune system, and accordingly, may protect against viral infections and perhaps other diseases. While some studies suggest the biological plausibility of vitamin C as an immune enhancer, human studies published to date are conflicting. Further, controlled clinical trials of appropriate statistical power would be necessary to determine if supplemental vitamin C boosts the immune system.

Food Sources of Vitamin C

As shown in the table below, different fruits and vegetables vary in their vitamin C content, but five servings (2½ cups) of fruits and vegetables should average out to about 200 mg of vitamin C. If you wish to check foods for their nutrient content, search the USDA food composition database.

Food                                     Serving                 Vitamin C (mg)
Orange juice                  ¾ cup (6 ounces)                62-93
Grapefruit juice              ¾ cup (6 ounces)                62-70
Orange                              1 medium                           70
Grapefruit                        ½ medium                             38
Strawberries                   1 cup, whole                          85
Tomato                             1 medium                             16
Sweet red pepper         ½ cup, raw chopped               95
Broccoli                            ½ cup, cooked                       51
Potato                               1 medium, baked                 17

Vitamin C Supplements

Vitamin C (L-ascorbic acid) is available in many forms, but there is little scientific evidence that any one form is better absorbed or more effective than another. Most experimental and clinical research uses ascorbic acid or sodium ascorbate.

Natural vs. synthetic vitamin C

Natural and synthetic L-ascorbic acid are chemically identical and there are no known differences in their biological activities or bioavailabilities

Kidney Stones

Because oxalate is a metabolite of vitamin C, there is some concern that high vitamin C intake could increase the risk of oxalate kidney stones. Some, but not all, studies have reported that supplemental vitamin C increases urinary oxalate levels. Whether any increase in oxalate levels would translate to an elevation in risk for kidney stones has been examined in epidemiological studies. Two large prospective studies, one following 45,251 men for six years and the other following 85,557 women for 14 years, reported that consumption of ≥1,500 mg of vitamin C daily did not increase the risk of kidney stone formation compared to those consuming <250 mg daily. However, a more recent prospective study that followed 45,619 men for 14 years found that those who consumed ≥1,000 mg/day of vitamin C had a 41% higher risk of kidney stones compared to men consuming <90 mg of vitamin C daily—the current recommended dietary allowance (see RDA). In this study, low intakes (90-249 mg/day) of vitamin C (primarily from the diet) were also associated with a significantly elevated risk. Supplemental vitamin C intake was only weakly associated with increased risk of kidney stones in this study. Despite conflicting results, it may be prudent for individuals predisposed to oxalate kidney stone formation to avoid high-dose vitamin C supplementation.

Linus Pauling Institute Recommendations

For healthy men and women, the Linus Pauling Institute recommends a vitamin C intake of at least 400 mg daily—the amount that has been found to fully saturate plasma and circulating cells with vitamin C in young, healthy nonsmokers. Consuming at least five servings (2½ cups) of fruits and vegetables daily provides about 200 mg of vitamin C. Most multivitamin supplements provide 60 mg of vitamin C. To make sure you meet the Institute’s recommendation, supplemental vitamin C in two separate 250-mg doses taken in the morning and evening is recommended.

Older adults (65 years and older)

Although it is not yet known with certainty whether older adults have higher requirements for vitamin C than younger people, some older populations have been found to have vitamin C intakes considerably below the RDA of 75 and 90 mg/day for women and men, respectively. A vitamin C intake of at least 400 mg daily may be particularly important for older adults who are at higher risk for chronic diseases. In addition, a meta-analysis of 36 publications examining the relationship between vitamin C intake and plasma concentrations of vitamin C concluded that older adults (age 60-96 years) have considerably lower plasma levels of vitamin C following a certain intake of vitamin C compared with younger individuals (age 15-65 years), suggesting that older adults may have higher vitamin C requirements. Studies conducted at the National Institutes of Health indicated that plasma and circulating cells in healthy, young subjects attain maximal concentrations of vitamin C at a dose of about 400 mg/day—a dose much higher than the current RDA. Pharmacokinetic studies in older adults have not yet been conducted, but evidence suggests that the efficiency of one of the molecular mechanisms for the cellular uptake of vitamin C declines with age. Because maximizing blood levels of vitamin C may be important in protection against oxidative damage to cells and biological molecules, a vitamin C intake of at least 400 mg daily is particularly important for older adults who are at higher risk for chronic diseases caused, in part, by oxidative damage, such as heart disease, stroke, certain cancers, and cataract.

References:

1.  Carr AC, Frei B. Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr. 1999;69(6):1086-1107.

2.  Simon JA, Hudes ES. Serum ascorbic acid and gallbladder disease prevalence among US adults: the Third National Health and Nutrition Examination Survey (NHANES III). Arch Intern Med. 2000;160(7):931-936.

3.  Bruno RS, Leonard SW, Atkinson J, et al. Faster plasma vitamin E disappearance in smokers is normalized by vitamin C supplementation. Free Radic Biol Med. 2006;40(4):689-697.

4. Kennes B, Dumont I, Brohee D, Hubert C, Neve P. Effect of vitamin C supplements on cell-mediated immunity in old people. Gerontology. 1983;29(5):305-310

5.   U.S. Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 22. 2009. Available at: http://www.nal.usda.gov/fnic/foodcomp/search/. Accessed 11/7/09.

6.  Michels AJ, Joisher N, Hagen TM. Age-related decline of sodium-dependent ascorbic acid transport in isolated rat hepatocytes. Arch Biochem Biophys. 2003;410(1):112-120

Many of the health institution in the world, including The Committee on Diet, Nutrition, and Cancer, took a stand against use of vitamin C supplements to meet it’s recommendations.

I think that scientists who take this position have one of two reasons. One is a very good one. But the other, in my opinion, is not so good.

The studies that tie vitamin C to cancer prevention usually link foods containing vitamin C rather than the vitamin itself to reduce risk of cancer. There is always the possibility that it is something else in these foods, rather than the vitamin C, that is protecting our health. If this is the case, people who take a vitamin C pill rather than eat vitamin C-containing foods will miss the unknown protective substance. Personally, I think that it is probably the vitamin C itself that is protective, though I also believe that other substance in these same foods may have anti-cancer ability.

Of  course, ideally we should get our vitamin C from foods. But some people just don’t care for vegetables, which supply almost 40 percent of the vitamin C in the industrial countries diet. And some parents have tried, but failed, to to convince their children to eat more fresh fruits and vegetables.

I simply cannot see withholding a moderate vitamin C supplement when this is the case. I think it is unscientific to advocate a diet that contains 200 mg of  vitamin C a day, yet oppose a supplement of this amount for those people who do not eat eat foods rich in vitamin C.

I know that there is a long history of opposition to vitamin supplements. Unfortunately, it has become an automatic response among some nutritionists. I cannot go along with it though, because sometimes it doesn’t make sense.

Can Vitamin C Hurt?

For all the noise that has been made about vitamin C supplements, you would think there were dead bodies lined up next to bottles of vitamin C.

I learned from many research  that in high doses some nutrients can cause more side effects than some drugs. At high doses, a vitamin such as nicotinic acid (a version of the vitamin known as niacin) really is a drug. But when it came to vitamin C, the research led me in a different direction. Try as I might, I could only conclude  that vitamin C was one of the least toxic substances in the pharmacy.

First, I would like to tell you that, in general, the amount of vitamin C that has been reported to cause problems in some people is far beyond the level you would get by eating a diet  rich in fruits and vegetables. But even at high doses, toxic effects appear to be the exception rather than the rule.

But I would like to mention four problems that have been linked to very high doses of vitamin C:

1. Kidney stones and aggravation of gout,

2. Destruction of vitamin B-12,

3. Complications from lack of the enzyme G6PD,

The Kidney Connection

It is true that high doses of vitamin C may speed formation of kidney stones. I have my own experience in this case, when I got the first kidney stones disorder in 1994. This side effect may occur mostly among people who are especially prone to kidney stones. Remember, though, that not everyone who teds to develop kidney stones knows it.

How much vitamin C did it take to bring on kidney stones or the early signs of stones? According to some researches  I learned, this problem has been seen in people taking 4 or more grams of vitamin C every day.

The same process that make kidney stones more likely to form may also worsen gout. People who are susceptible to gout should also take note of these findings.

About Destruction of Vitamin B-12

It is also possible, but probably not likely, that vitamin C may destroy some of the vitamin B-12 in food.

Two decades ago, two scientists put together some laboratory equipment to mimic digestion. They reported that under these “test-tube” conditions, a 500 mg supplement of vitamin C destroyed a high percentage of the vitamin B-12 in food.

When another scientist directly studied this issue in human subjects, the results were different. This researcher examined vitamin B-12 levels in the blood of people who had been taking at least 500 mg of vitamin C daily. He found that only three of the ninety people tested had low levels of vitamin B-12. These three, all fifty to sixty years of age, had been taking a minimum of 1000 mg of vitamin C with each meal for more than three years.

There is one more fact to note:  scientists believe that less vitamin B-12 will be destroyed if the vitamin C is taken two or more hours after eating.

If You Have G6PD Deficiency

High doses of vitamin C can be fatal for you. I found a case that a man who had been given 80 grams of vitamin C for two days as a treatment burns. He died a few weeks later.

It turned out that this patient had a deficiency of the enzyme G6PD. It stand for glucose-6-phosphate dehydrogenase. As its name implies, this enzyme is used in metabolism of glucose, a type of sugar.

Although this man had been given enormous amount of vitamin C, scientists are concerned that others with G6PD deficiency may be sensitive to smaller amounts. If you have this condition, you should be aware of this concern.

About 10 percent of  Afro-American males have mild G6PD deficiency. A smaller percentage of black females are affected, as are a few Caucasians. Screening tests for this condition are readily available.

Regarding the story of vitamin C and cancer, please click here.

(a  lyric written by John Denver).