Grading vitamin C.

Some of us take it to prevent colds. Others to help ward off heart disease and cancer. Seniors use it to stop cataracts.

Multivitamins aside, we take more vitamin C than any other supplement. Does it do us any good?

In some cases, maybe; in most, there's not enough good research to tell. Here's a vitamin C report card. (See p. 12 for our guide to taking vitamin C.)

THE COMMON COLD PREVENTING: F

REDUCING DURATION: B

RELIEVING SYMPTOMS: B

Nobel Prize winner Linus Pauling, who died last August at the age of 93, took vitamin C to prevent colds. So do millions of others.

It doesn't work.

Since 1956, there have been at least 12 randomized, double-blind, placebocontrolled studies of whether vitamin C can prevent colds. That means researchers compared people taking C to people taking a placebo (an inactive look-alike pill). All in all, more than 7,400 people in at least six countries have been given anywhere from 65 mg to three grams (3,000 mg) of vitamin C or a placebo every day for eight weeks to nine months.

In none of the 12 studies did vitamin C prevent colds from occurring.

But don't toss that bottle yet. While C won't prevent colds, in some studies it helped people weather them better.

"The data do show a reduction in the severity and duration of colds," notes Adrianne Bendich, a clinical research scientist with Hoffmann-La Roche, the leading manufacturer of vitamin C.

For instance, although C-taking U.S. Marines in a 1979 study had no fewer colds, they did report a slight decrease in the severity of symptoms like coughing, fever, chills, runny noses, and sore throats.(1)

And among 95 pairs of Australian identical twins studied in 1981, 1,000 mg of vitamin C a day cut the length of the average cold from almost 6 1/2 days to a tad over five days.(2) (In both cases, the volunteers were taking C before their colds developed.)

Those results are nothing to sneeze at. Colds are one of the major causes of lost days at work or school in the U.S.

RAISING "GOOD" CHOLESTEROL: C

When researcher Judith Hallfrisch and colleagues recently measured the levels of vitamin C in the blood of 511 men in the Baltimore Longitudinal Study of Aging, she saw that those with more C had higher levels of HDL ("good") cholesterol.(3)

But Hallfrisch's results--and others like them--don't mean that taking vitamin C supplements causes HDL to rise. People with more C in their blood may be more likely to do other things that raise their HDL (like exercising or losing weight).

In fact, the only well-designed study in the U.S. in which researchers actually gave people vitamin C supplements and then measured their cholesterol came up empty.(4)

PREVENTING LDL OXIDATION: C

Low-density lipoprotein (you probably know it as LDL, or "bad" cholesterol) can become oxidized, just as the butter in your fridge can go rancid. And that may enable it to invade the walls of the arteries that nourish your heart. From there, it can build the "plaques" that block the flow of blood.

"There's a plausible case to be made for antioxidants interfering with the oxidation of LDL and thus preventing atherosclerosis," says Robert Nicolosi, director of the Cardiovascular Research Center at the University of Massachusetts at Lowell.

"But among the antioxidants," he adds, "the weakest evidence is for vitamin C. It's not anywhere near as strong as the evidence for vitamin E, with beta-carotene coming in second."

Unlike vitamin E and beta-carotene, vitamin C is water-soluble. That makes it unable to penetrate the fatty LDL lipoprotein molecule, explains Nicolosi.

If high levels of C do anything, he says, "they may protect vitamin E from being depleted, so that more E hangs around and gets incorporated into LDL and prevents its oxidation."(5)

LOWERING BLOOD PRESSURE: C

In two very small studies, when a total of 32 people with either normal or borderline-high blood pressure were given 1,000 mg a day of vitamin C for four to six weeks, their average systolic blood pressure (the first number) dropped by four to eight points.(4)(6)

But a third study--using 400 mg a day for four weeks--showed no reduction.(7)

Those results are "equivocal," says Robert Nicolosi. "We need both more animal and human clinical trial data, and it's not out there yet."

PREVENTING CATARACTS: C

Cataracts are the leading cause of blindness in the world. In this country, removing them is the most common surgery performed on people over the age of 65.

A cataract--or clouding of the lens--occurs when proteins in the eye become oxidized, possibly by exposure to the sun or to rogue molecules (free radicals) produced in the body.

"Since antioxidants like vitamin C extinguish free radicals before they can do harm, they might be able to prevent cataracts," says researcher Paul Jacques of the U.S. Department of Agriculture's Human Nutrition Research Center on Aging at Tufts University in Boston.

But the evidence is, well, clouded.

Some researchers have observed that people who get more vitamin C seem to have a lower risk of developing cataracts. Other studies find no relationship.

Only one study has actually tested vitamin C's ability to prevent cataracts. Researchers in China fed 2,068 middle-aged and older people either 120 mg a day of vitamin C or a placebo. After five years, the C-takers had no fewer cataracts than the placebo-takers.(8)

But the people being studied had poor diets, so the results may not apply to well-nourished Americans. What's more, it may take a larger dose or a longer time for vitamin C to work.

PROTECTING AGAINST CANCER: C

"More than a hundred studies around the world have observed that people who eat diets rich in fruits and vegetables are about half as likely to develop cancer as people who eat few fruits and vegetables," notes nutrition epidemiologist John Potter of the University of Minnesota.

But is it the C in those foods that's doing the protecting? Maybe. Maybe not.

Vitamin C can prevent some tumors in laboratory animals, and it may prevent cancer-causing nitrosamines from forming in people's stomachs. But overall, the human evidence is discouraging.

Among the 89,000 women being monitored since 1980 by Harvard's Nurses' Health Study, for example, those who chose to take at least 750 mg a day of C had no lower risk of breast cancer than non-C-taking nurses.(9)

And last July, researchers at Dartmouth Medical School found that giving people 1,000 mg a day of vitamin C didn't reduce the number of (sometimes) pre-cancerous colon polyps in those who had already had at least one polyp removed.(10)

"We have to be careful about saying that it's the vitamin C or the beta-carotene or the vitamin E in fruits and vegetables that's responsible for their prevention of cancer," says Mark Levine, a vitamin C researcher at the National Institutes of Health.

STRENGTHENING THE IMMUNE SYSTEM: C

Vitamin C is vital for the normal functioning of the immune system, which helps our bodies fight off disease. But while there have been "a number of test tube studies suggesting that extra vitamin C might increase the immune response," says Greg Coodley of the Oregon Health Sciences University, "there are no studies showing that taking vitamin C protects people from getting sick."

For example, some test-tube studies at the Linus Pauling Institute in Palo Alto, California, have suggested that vitamin C may inhibit the HIV virus, which is responsible for AIDS.

"But lots of things that inhibit the virus in the lab don't work in humans," says Coodley.

So far, there haven't been any good human studies of vitamin C and HIV.

(1)Journal of the American Medical Association 241: 908, 1979.

(2)Medical Journal of Australia 2: 411, 1981.

(3)American Journal of Clinical Nutrition 60: 100, 1994.

(4)Nutrition Research 11: 405, 1991.

(5)Journal of Lipid Research 33: 385, 1992.

(6)American Journal of Clinical Nutrition 53: 322S, 1991.

(7)Journal of Human Hypertension 7: 403 1993.

(8)Archives of Ophthalmology 111: 1246, 1993.

(9)New England Journal of Medicine 329: 234, 1993.

(10)New England Journal of Medicine 331: 141, 1994.

KEY TO GRADES

A -- Yes. Convincing evidence

B -- Probably. Consistent, but not yet convincing, evidence

C -- Too early to tell. Not yet enough good evidence

F -- No. Disproven

just the VITAMIN C facts

So you've decided to hedge your bets and take some vitamin C (see p. 10). Now you've got to figure out how much of what is best.

* How much? The U.S. Recommended Daily Allowance (USRDA) for vitamin C is 60 mg. So is the Daily Value (DV), which appears on food labels. That turns out to be about what we get from our food.

But "for most people, tissue saturation is reached with about 250 to 500 mg a day," says researcher Balz Frei of Boston University.

And most intervention trials, in which researchers give vitamin C to volunteers and then see what happens to them, use one gram (1,000 mg) or less.

* Natural or synthetic? The word "natural" on a vitamin C bottle doesn't mean much. That's because the FDA doesn't regulate the term. While your "natural" C could be all natural, more likely it's a blend of mostly synthetic C (usually made from corn starch) with a little natural C (probably rose hips or acerola berries).

* With rose hips, acerola berries, or bioflavonoids? There's no good evidence either for or against them.

With rose hips and acerola, "it's more a matter of consumer preference than scientific evidence," says David Mastroianni of Schiff Products, the company that first added rose hips to vitamin C.

Bioflavonoids like hesperidin and rutin, which are found in fruits and other vitamin-C-rich plants, suffer from a long history of conflicting and imprecise research.

* Time-release? Researchers don't know if it's any better.

* What About Side Effects? Vitamin C appears to be safe, even at doses of several thousand milligrams a day. The most common reaction: diarrhea.

"About ten percent of my volunteers get diarrhea when they take 500 mg to 2,000 mg at a time," reports vitamin C researcher Carol Johnston of Arizona State University. The solution? Take smaller amounts spread out over the course of the day.

Taking C doesn't appear to promote kidney stones in people who aren't prone to getting them. But it could harm people with hemochromatosis, who can easily absorb toxic levels of iron. (Vitamin C improves iron absorption.) To play it safe, "those people shouldn't take vitamin C supplements," says Mark Levine, a vitamin researcher at the National Institutes of Health.

Seeing C

How easy is it to get your vitamin C from food? We thought you'd never ask. Here are some of the main sources.

Food (uncooked, unless                   Vitamin
otherwise indicated)                     C (mg)
kiwi fruit (2)                            145
orange juice (1 cup)(*)                   105
papaya (1 cup)                             87
strawberries (1 cup)                       83
orange (1)                                 82
broccoli, raw (1 cup)                      79
grapefruit juice, canned (1 cup)           76
green or red pepper (1/2)                  76
vegetable juice cocktail (1 cup)           67
broccoli, cooked (1/2 cup)                 63
apple or grape juice, fortified (1 cup)    60
cantaloupe (1/4)                           57
brussels sprouts, cooked (1/2 cup)         53
grapefruit (1/2)                           53
tangerines (2)                             52
snow peas (1/2 cup)                        51
cauliflower, cooked (2/3 cup)              47
tomato juice (1 cup)                       44
cabbage, shredded (1 cup)                  40
mango (1 cup)                              39
kale, cooked (2/3 cup)                     35
raspberries (1 cup)                        35
honeydew (1/10)                            33
sweet potato, baked (1)                    32
pineapple juice, canned (1 cup)            27
watermelon (2 cups)                        27
spinach, raw (1 1/2 cups)                  24
pineapple (1 cup)                          22
lettuce, romaine (1 1/2 cups)              20
parsley (1/4 cup)                          20
potato, baked, with skin (1)               19
radishes (7)                               19
blueberries (1 cup)                        18
tomato (1/2 cup)                           16
tomato sauce (1/2 cup)                     16
potato, baked, without skin (1)            15
apricots (4)                               14
sauerkraut, canned (1/2 cup)               14
spaghetti sauce (1/2 cup)                  14
plums (2)                                  13
peas, cooked (1/2 cup)                     12
banana (1)                                 11
peaches (2)                                11
prune juice (1 cup)                        11
asparagus (5 spears)                       10
cherries (1 cup)                           10
collard greens, cooked (2/3 cup)           10
apple (1)                                   9
pear (1) or carrot (1)                      7
nectarine (1)                               8
spinach, cooked (1/2 cup)                   8
grapes (1 1/2 cups)                         6
beets, cooked (1/2 cup)                     5
corn, cooked (1/2 cup)                      5

(*)Average of refrigerated (from concentrate and not from concentrate) and frozen.

Sources: USDA Handbook 8 and Florida Department of Citrus.