vitamin C
What can high-vitamin C foods do for you?
Help protect cells from free radical damage
Lower your cancer risk
Regenerate your vitamin E supplies
Improve iron absorption
What events can indicate a need for more high-vitamin C foods?
Poor wound healing
Frequent colds or infections
Lung-related problems
Excellent sources of vitamin C include: parsley, broccoli, bell pepper, strawberries, oranges, lemon juice, papaya, cauliflower, kale, mustard greens, and Brussels sprouts.
Description
What is vitamin C?
Because of its widespread use as a dietary supplement, vitamin C may be more familiar to the general public than any other nutrient. Studies indicate that more than 40% of older individuals in the U.S. take vitamin C supplements; and in some regions of the country, almost 25% of all adults, regardless of age, take vitamin C. Outside of a multivitamin, vitamin C is also the most popular supplement among some groups of registered dietitians, and 80% of the dietitians who take vitamin C take more than 250 milligrams. Why is this nutrient so popular?
Vitamin C, also called ascorbic acid, is a water-soluble nutrient that is easily excreted from the body when not needed. It's so critical to living creatures that almost all mammals can use their own cells to make it. Humans, gorillas, chimps, bats, guinea pigs and birds are some of the few animals that cannot make vitamin C inside of their own bodies.
Humans vary greatly in their vitamin C requirement. It's natural for one person to need 10 times as much vitamin C as another person; and a person's age and health status can dramatically change his or her need for vitamin C. The amount of vitamin C found in food varies as dramatically as our human requirement. In general, an unripe food is much lower in vitamin C than a ripe one, but provided that the food is ripe, the vitamin C content is higher when the food is younger at the time of harvest.
How it Functions
What is the function of vitamin C?
Vitamin C serves a predominantly protective role in the body. As early as the 1700's, vitamin C was referred to as the "antiscorbutic factor," since it helped prevent the disease called scurvy. This disease was first discovered in British sailors, whose sea voyages left them far away from natural surroundings for long periods of time. Their body stores of vitamin C fell below 300 milligrams, and their gums and skin lost the protective effects of vitamin C. Recognizing limes as a good shipboard source of vitamin C, the British sailors became known as "limeys" for carrying large stores of limes aboard ship.
The protective role of vitamin C goes far beyond our skin and gums. Cardiovascular diseases, cancers, joint diseases and cataracts are all associated with vitamin C deficiency and can be partly prevented by optimal intake of vitamin C. Vitamin C achieves much of its protective effect by functioning as an antioxidant and preventing oxygen-based damage to our cells. Structures that contain fat (like the lipoprotein molecules that carry fat around our body) are particularly dependent on vitamin C for protection.
Deficiency Symptoms
What are deficiency symptoms for vitamin C?
Full-blown symptoms of the vitamin C deficiency disease called scurvy—including bleeding gums and skin discoloration due to ruptured blood vessels—are rare in the U.S. Poor wound healing, however, is not rare, and can be a symptom of vitamin C deficiency. Weak immune function, including susceptibility to colds and other infections, can also be a telltale sign of vitamin C deficiency. Since the lining of our respiratory tract also depend heavily on vitamin C for protection, respiratory infection and other lung-related conditions can also be symptomatic of vitamin C deficiency.
Toxicity Symptoms
What are toxicity symptoms for vitamin C?
There are very few research studies that document vitamin C toxicity at any level of supplementation, and there are no documented toxicity effects whatsoever for vitamin C in relation to food and diet. At high supplemental doses involving 5 or more grams of vitamin C, diarrhea can result from the fluid in the intestine becoming too concentrated ("osmotic diarrhea").
Large supplemental doses of vitamin C can also increase levels of uric acid in the urine, because vitamin C can be broken down into uric acid. However, it is not clear that increased uric acid in the urine can increase a person's risk of forming uric acid kidney stones.
Finally, vitamin C can increase a person's absorption of iron from plant foods; and persons who have health problems related to excess free iron in their cells may want to consider avoiding high supplemental doses of vitamin C. It is important to remember that all of the above toxicity-related issues involve vitamin C in supplemental form, not as it naturally occurs in food.
In 2000, the National Academy of Sciences set a Tolerable Upper Intake Level (UL) for vitamin C at 2,000 milligrams (2 grams) for adults 19 years or older.
Impact of Cooking, Storage and Processing
How do cooking, storage, or processing affect vitamin C?
Vitamin C is highly sensitive to air, water, and temperature. About 25% of the vitamin C in vegetables can be lost simply by blanching (boiling or steaming the food for a few minutes). This same degree of loss occurs in the freezing and unthawing of vegetables and fruits. Cooking of vegetables and fruits for longer periods of time (10-20 minutes) can result in a loss of over one half the total vitamin C content. When fruits and vegetables are canned and then reheated, only 1/3 of the original vitamin C content may be left. Consumption of vitamin C-rich foods in their fresh, raw form is the best way to maximize vitamin C intake.
Factors that Affect Function
What factors might contribute to a deficiency of vitamin C?
Poor intake of vitamin C-rich vegetables and fruits is a common contributor to vitamin C deficiency. In the U.S., one third of all adults get less vitamin C from their diet than is recommended by the National Academy of Sciences, and 1 out of every 6 adults gets less than half the amount recommended. Smoking and exposure to second hand smoke also increase the risk of vitamin C deficiency.
The body's immune and detoxification systems make special use of vitamin C, and overload in either of these systems can increase risk of deficiency. The immune system relies on a wide variety of mechanisms to help protect the body from infection, including white blood cells, complement proteins, and interferons; and vitamin C is especially important in the function of these immune components.
Vitamin C is also critical during the first phase of the body's detoxification process. This process occurs in many types of tissue, but it is especially active in the liver. When the body is exposed to toxins, vitamin C is often required for the body to begin processing the toxins for elimination. Excessive toxic exposure is therefore a risk factor for vitamin C deficiency.
Nutrient Interactions
How do other nutrients interact with vitamin C?
Vitamin C has significant interactions with several key minerals in the body.
Supplemental intake of vitamin C at gram-level doses can interfere with copper metabolism. Conversely, vitamin C can significantly enhance iron uptake and metabolism, even at food-level amounts.
Vitamin C also has important interactions with other vitamins. Excessive intake of vitamin A, for example, is less toxic to the body when vitamin C is readily available. Vitamin C is involved in the regeneration of vitamin E, and these two vitamins appear to work together in their antioxidant effect.
Health Conditions
What health conditions require special emphasis on vitamin C?
Most forms of cardiovascular disease, joint disease, cancer, eye disease, thyroid disease, liver disease, and lung disease require special emphasis on vitamin C intake. The process of aging itself requires special attention to vitamin C. In addition to these broader categories, several specific health conditions also require special emphasis on vitamin C. These specific health conditions include:
Acne
Alcoholism
Alzheimer's disease
Asthma
Autism
Depression
Diabetes
Irritable bowel disease
Parkinson's disease
Food Sources
What foods provide vitamin C?
Excellent food sources of vitamin C include broccoli, bell peppers, parsley, Brussels sprouts, cauliflower, lemon juice, strawberries, mustard greens, kiwifruit, papaya, kale, cabbage, romaine lettuce, turnip greens, oranges, cantaloupe, summer squash, grapefruit, pineapple, chard, tomatoes, collard greens, raspberries, spinach, green beans, fennel, cranberries, asparagus, watermelon, and winter squash.
Introduction to Nutrient Rating System Chart
In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the World's Healthiest Foods that are either an excellent, very good, or good source of vitamin C. Next to each food name, you'll find the serving size we used to calculate the food's nutrient composition, the calories contained in the serving, the amount of vitamin C contained in one serving size of the food, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's
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