Also known as ascorbic acid and ascorbate, vitamin C plays a role in the production of bone and connective tissue, certain hormones, and substances that transmit nerve impulses. It also helps the body absorb iron, the liver detoxify dangerous chemicals, and white blood cells fight infection. Finally, it is an antioxidant, thought to promote longevity.
Citrus fruits are a good source of vitamin C; so are potatoes, peppers, strawberries, melons, tomatoes, broccoli, cauliflower, brussels sprouts, cabbage, and spinach. Vitamin C is also added to many packaged fruit juices and snacks.
A shortage of vitamin C causes scurvy, whose chief symptoms are bleeding of the gums, bleeding under the skin (bruising), and extreme weakness.
Too much vitamin C can lead to gastrointestinal disturbances (nausea, diarrhea), kidney stones, and excess iron absorption.
Vitamin C and Cancer*
People who eat a lot of vitamin-C-rich fruits and vegetables are at lower risk for mouth, throat, stomach, and premenopausal breast cancer. Neverthless, vitamin-C supplements haven't been shown to lower such risks¾the benefit may come from something else in these foods.
Vitamin C and Heart Disease*
Neither dietary nor supplemental vitamin C appears to prevent coronary heart disease (CHD) or to help patients who already have CHD. Some researchers believe that vitamins C and E in combination may ward off CHD, but studies have not yet been completed.
Our latest source for the cancer and heart-disease summaries is a review of more than 150 scientific papers, "Vitamins for Chronic Disease Prevention in Adults," published by Drs. Kathleen M. Fairfield and Robert H. Fletcher in the June 19, 2002, Journal of the American Medical Association (JAMA). Reprints can be downloaded (for a fee) from the JAMA Web site at www.jama.ama-assn.org.
Your Daily Allowance
Diet Power sets your Personal Daily Allowance (PDA) of vitamin C at the Food and Nutrition Board's (FNB's) Recommended Dietary Allowance (RDA). In April 2000 the FNB raised the RDAs for this nutrient by 8 to 50 percent, depending on sex and life stage. For most men the RDA is now 90 milligrams; for most women, 75 milligrams. For boys 14** to 18, however, it's 75 milligrams; and for girls in that age group it's 65 milligrams. For pregnant women age 18 or under it's 80 milligrams; for those age 19 to 50 it's 85 milligrams. During lactation it's 115 milligrams for mothers 18 and younger and 120 milligrams for those age 19 to 50. (In the rare event that you are over 50 and pregnant or lactating, Diet Power uses the PDA for the 19-to-50 age group.)
In addition, there is strong evidence that smokers need extra vitamin C. If you check the "I smoke" box on your Personal Information Form, Diet Power will increase your PDA by 35 milligrams.*** (This, too, reflects the recent RDA change. Formerly, smokers of all ages, male and female, got the same RDA: 100 milligrams.)
All of these figures are minimums. It is generally considered safe to get more vitamin C than your body needs¾provided you get it from foods, and then only up to a point. A 1998 British study found that the popular practice of taking daily 500-milligram supplements could damage part of the cells' DNA. The finding corroborated a longstanding claim by some experts that vitamin-C supplements may eventually damage the heart and other organs.
Please remember that Diet Power is not designed for people under 15.
The 35-milligram increase doesn't apply to "passive" smokers, but the FNB urges "nonsmokers regularly exposed to tobacco smoke" to make sure they meet their RDA for vitamin C.
In April 2000, for the first time, the FNB announced a Tolerable Upper Intake Level (UL) for vitamin C. People 14**** to 18 years old should get no more than 1800 milligrams per day; people 19 and older, no more than 2000 milligrams per day.
**** Please remember that Diet Power is not designed for people under 15.
Revising Your Allowance
Diet Power automatically sets your Personal Daily Allowance of vitamin C when you enroll in the program, but you can change your PDA to reflect your physician's recommendation. See Personal Daily Allowances, Editing Your.
Color Coding of This Nutrient
The vitamin-C bar in your personal Nutrient History is:
· blue for "good" if you've logged 100 to 200 percent of your PDA
· red for "bad" if you've logged less than 100 percent of your PDA or more than the Tolerable Upper Intake Level (UL)
· yellow for "caution" if you've logged more than 200 percent of your PDA
· missing if you've logged no vitamin C.
In the nutrient profile of a food or recipe, the vitamin-C bar is:
· green for "good" if getting your entire PDA of calories from this item would give you more than 150 percent of your PDA of vitamin C
· magenta for "bad" if getting all your calories from the item would give you less than 50 percent of your PDA of vitamin C
· blue for "neutral" otherwise
· missing if the amount of vitamin C is either zero or (when the term Vitamin C is grayed out) unknown.
How Complete Are Diet Power's Vitamin-C Readings?
For the 8500 generic items in the Food Dictionary: very complete. Only 0.3 percent list their vitamin-C content as "unknown."
For the 2500 chain-restaurant items: not terribly complete. About 38 percent list vitamin C as "unknown."
For all 11,000 items combined: fairly complete. About 8 percent list vitamin C as "unknown."
These figures mean that if you frequently log chain-restaurant foods (or user-added foods with missing vitamin-C readings), your Nutrient History may underreport your intake of vitamin C by a few points.
To see whether a particular food has a vitamin-C reading, open the Food Dictionary and check the food's nutrient profile. If you find a question mark beside "Vitamin C," it means the amount is unknown. (To see all foods with unknown vitamin-C readings, click the dictionary's PowerFoods tab and sort the foods by vitamin-C power; then scroll toward the bottom of the list until you see foods with question marks in the "Power Rating" column.)
Vitamin C on Food Labels
Food labels are required to report vitamin-C content as a percentage of Daily Value.
The Daily Value for vitamin C is 60 milligrams. This amount is not necessarily right for you, however¾it's a rough estimate meant to accommodate most of the U.S. population. (Remember, too, that the Daily Value does not yet reflect the April 2000 increase in this vitamin's RDAs. See above.)
For more on label regulations, see Labels, Food.