Part 3 of a six-part series on key vitamins.
Vitamin C seems almost a nutritional has-been in media attention. Yet it remains a top seller. Despite that, there are still many people who shortchange themselves. Vitamin C garners attention mostly for heading off the full-fledged assault of the common cold and sometimes for its anticancer promise, and rightfully so. But vitamin C's role in good health goes beyond boosting the immune system. EN takes a closer look.
C for Cellular Bodyguard. Vitamin C is a powerful antioxidant that helps neutralize free radicals produced by exposure to the environment--sunlight, smog, and smoking--and our bodies.
We employ a sophisticated system to neutralize free radicals, but it wanes with age. The resulting cell damage is thought to fuel chronic conditions such as heart disease, cancer, infections and eye diseases.
Some experts believe vitamin C's synergy with vitamin E, also a formidable antioxidant, is key to curtailing chronic conditions. After vitamin E is finished fending off a free radical, vitamin C regenerates E, enabling it to carry out even more damage control.
Can C Curb Cancer? When it comes to preventing cancer, it's tempting to look for magic bullets like a vitamin C supplement. After all, studies from around the globe consistently show a link between diets rich in vitamin C and a reduced risk of many types of cancer, particularly those of the gastrointestinal tract (mouth, pharynx and esophagus), pancreas, lung and cervix.
The strongest connection for vitamin C's anti-cancer benefit is with stomach cancer. Researchers at the San Francisco Veterans Administration Medical Center recently found that high blood levels of vitamin C protect against infection with H. pylori, the bacterium that causes most ulcers and increases the risk of stomach cancer.
Vitamin C also combats stomach cancer by blocking production of nitrosamines, carcinogens that form when nitrates in foods like cured meat (and in saliva) combine with compounds in the stomach's digestive juices.
But while vitamin C seems to be a powerful player, it is likely that it's the overall mix of nutrients and phytonutrients in C-rich foods--mostly fruits and vegetables--that's really responsible for cancer risk reduction.
C and Colds. Vitamin C is necessary to form the white blood cells that fight infections--including the common cold--but it can't prevent the cold virus from taking hold in the absence of a robust immune system. Can C make you feel better once you have the sniffles? Possibly. Several studies have found that extremely large doses (2,000 milligrams a day) of vitamin C can reduce the severity and duration of cold symptoms.
C for Heart and Mind. Population studies suggest that eating foods rich in antioxidant nutrients, including vitamin C, protects against heart disease. Getting at least 220 milligrams of vitamin C a day was more protective against heart disease than 141 milligrams a day or less, according to a recent study from Korea. In a recent Dutch study, researchers found that those with the lowest intakes of C were 30% more likely to suffer a stroke than those with the highest.
Researchers have a number of theories as to how vitamin C heads off heart attacks and strokes. C is able to thwart the oxidation of low-density lipoproteins (LDL's, the 'bad' cholesterol), thereby protecting against clogged arteries in the heart and the brain. C also shores up blood vessel walls, promoting good circulation. And a number of studies show that vitamin C can actually prevent blood vessels from constricting and cutting off the flow of blood to the heart and brain.
Oh, Say, Can You C? Those same nasty free radicals that may fuel cancer and heart disease can also oxidize the cells in the lens of your eye, triggering the formation of cataracts. Vitamin C alone or with other antioxidants combats this oxidation.
Researchers at Tufts University and Harvard University, who studied nearly 250 women with no history of cataracts, found that those who took vitamin C supplements for at least 10 years were 77% less likely to show the initial signs of cataracts and 83% less likely to have moderate opacities than those who took no supplemental C. It's uncertain how much vitamin C is necessary to saturate eye tissues, but experts estimate it's between 150 and 250 milligrams a day.
In combination with other nutrients, vitamin C has also shown benefit in slowing the progression of age-related macular degeneration, a condition that damages the retina and can destroy vision.
Vitamin C and Gallbladder Disease.
When blood levels of vitamin C are insufficient, the body slows down the conversion of cholesterol to bile acids. As cholesterol builds up in bile, the risk of gallstones rises. Supporting this relationship, University of California researchers have found a significant reduction in gallbladder disease among postmenopausal women who take vitamin C supplements.
Getting Enough C? The body doesn't store vitamin C, so you need some most every day. The current Recommended Dietary Allowance (RDA) for vitamin C is 75 milligrams a day for women and 90 for men, with smokers requiring an additional 35 milligrams daily. (The maximum safe dose is set at 2,000 milligrams a day.) But while the RDA is more than enough to prevent scurvy (vitamin C deficiency), it might not be enough for optimal health.
A study by the National Institutes of Health recommends 200 milligrams of vitamin C daily. A joint panel of the American Aging Association and the American College of Clinical Gerontology also cites 200 milligrams of C as a daily goal for adults over 65. But some experts advocate even more.
'Getting between 200 and 500 milligrams of vitamin C a day is certainly closer to an optimal intake for promoting health and reducing the risk of some chronic diseases than the RDA,' maintains Jeffrey Blumberg, Ph.D., chief of the Antioxidants Research Lab at Tufts University in Boston. While Blumberg cautions that more clinical trials are needed, there is evidence that more vitamin C than the RDA may be beneficial for certain people:
* A new study from Johns Hopkins suggests that a combination of vitamins C and E helps you dodge Alzheimer's disease. In the three-year study, people taking at least 500 milligrams of vitamin C plus 400 International Units of vitamin E daily were less likely to develop Alzheimer's.
* A report from the University of California at Berkeley recently found that nonsmokers who took 500 milligrams of vitamin C a day reduced the oxidative stress from second-hand smoke.
* Supplementing with 500 milligrams of vitamin C every day helped reduce high blood pressure in participants in Boston University and Oregon State University studies. Vitamin C may protect a natural compound in the body that promotes normal blood pressure.
The Bottom Line. For now, EN advises getting at least 200 milligrams of vitamin C every day. And it's not unreasonable to get up to 500; more than that has not shown benefit, other than possibly staving off a worsening of cold symptoms.
Moreover, it's not that hard to get 200 milligrams if you eat the recommended five-plus servings of fruits and vegetables daily--with at least one being citrus--and take a multivitamin with the Daily Value of 60 milligrams of C.
Searching for C Food Vitamin C (milligrams) Sweet red pepper, raw, 1/2 cup 141 Apricot nectar, canned, 8 fl oz 136 Orange juice, fresh-squeezed, 93 6 fl oz Strawberries, fresh, 1 cup 84 Orange, 1 medium 75 Orange juice, from concentrate, 73 6 fl oz Kiwifruit, 1 medium 71 Grapefruit juice, from concentrate, 63 6 fl oz Cantaloupe, 1 cup cubes 59 Vegetable juice cocktail, 6 fl oz 50 Broccoli, cooked, 1/2 cup 50 Brussels sprouts, cooked, 1/2 cup 49 Raspberries, fresh, 1 cup 41 Grapefruit, 1/2 medium 40 Pineapple, 1/2 cup tidbits 28 Cauliflower, cooked, 1/2 cup 28 Tangerine, 1 medium 26 Potato, baked with skin, 1 medium 19 Tomato, raw, 1 medium 16 fl oz = fluid ounces Source: USDA Database, Release 16, 2003
