Wednesday, July 16, 2008

Vitamin C: Functions, Daily Needs, Excessive Intake

Vitamin C was discovered in 1932. It is also known as Ascorbic Acid. Ascorbic is the Latin word for "without scurvy". Scurvy is one of the oldest known disease caused by nutrient deficiency. Scurvy was first described by the Egyptians in 1550 B.C. Prior to the discovery of vitamin C, scurvy was responsible for the death of most sailors on prolonged sea voyages where they mainly eat cereals and meat. Eventually, lime and lemon were added to their diets and scurvy stopped haunting the sailors. The symptoms of scurvy includes bleeding gums, pinpoint hemorrhages under the skin, dry scaly skin, swollen and tender joints, aching bones, muscle cramps, depression, swollen legs and arms, loosened teeth, etc.

Humans must depend on their diets to obtain adequate vitamin C, since it cannot be manufactured by the human body. Vitamin C is a water soluble vitamin, excess vitamin C cannot be stored by the body and will be excreted. Therefore, it is important to ensure adequate vitamin C intake daily.

Functions of Vitamin C

1. Formation and Maintenance of Collagen

Collagen is the basis for connective tissue, the most abundant tissue in the body. Collagen is found in bones, teeth, tendons, skin, cornea of the eye, blood vessel walls. Collagen also promotes the healing of wounds, bruises, hemorrhages, bleeding gums and fractures. It plays a role in immunity by forming a protective barrier between infections or disease and the surrounding healthy tissues. Recent research showed that vitamin C cannot prevent colds effectively, but can reduce the severity and duration of a cold. Therefore, vitamin C has an important role in strengthening bones and teeth, having healthy skin and blood vessels, wound healing, and immunity.

2. Antioxidant

Smoking, air pollution, contaminants, caffeine are substances which leads to free radicals formation. Free radicals are related to atherosclerosis, diabetes, cancer, cataracts, Parkinson's disease, Alzheimer's disease etc. In addition, free radicals are linked to the aging. Vitamin C has antioxidant effect, thus has the ability to destroy free radicals. Research indicated that vitamin C can prevent or slow down the progression of cancer, especially cancer of the stomach, esophagus, lung, cervix, and liver. It can also inhibit the formation of nitrosamine, a potent cancer-causing agent. Nitrosamines are formed from nitrites which are found in cured meats, like ham, luncheon meat, sausage, bacon etc. Moreover, vitamin C can delay the aging process. Under normal circumstance, 250 mg of vitamin C daily has a strong
antioxidant effect.

3. Enhancement of Iron Absorption

When foods containing iron and vitamin C are taken together, iron absorption is enhanced. Therefore, vitamin C can prevent anemia. The symptoms of anemia include persistent fatigue, lowered immunity, dizziness etc. Children with anemia will become tired easily, have difficulty concentrating, poor immunity, and poor learning ability.

Daily Needs of Vitamin C

The United States Recommended Dietary Allowance (RDA) of vitamin C is 60 mg per day.
Adequate levels can be obtained by eating more vegetables and fruits. We need two to three servings (one serving is equivalent to one orange or apple or banana or kiwi fruit etc.) of fruit daily and 6 taels (240 grams) of vegetables daily. Vitamin C is lost when heated and during the storage process, especially when stored at temperature over 4C(40F). Therefore, do not overcook or store vegetables for too long. A reasonable amount of vegetables should be prepared at each meal to prevent having leftovers. Vegetables should be wrapped in plastics, stored in the refrigerator and consumed quickly.

In 1996, the United States Olympic Committee raised athletes' vitamin C requirement to 250 - 1000 mg per day because athletes are under more stress than the general population. Smoking not only has no health benefit, it will also lead to lose of vitamin C. In addition, smoker's vitamin C absorption is weaker, therefore, they need 200 mg per day.

Comparison Of Vitamin C In 100 Grams Of Fresh And Boiled Vegetables

Fresh: 93.2 mg
Boiled: 74.6 mg

Fresh: 32.2 mg
Boiled: 20.1 mg

Fresh: 28.1 mg
Cooked: 9.8 mg

Vitamin C Contents In Foods

Vitamin C content in vegetables

Vegetable (100g)Vitamin C (mg)
Sweet red pepper 190
Kai Lan 107
Broccoli 93
Watercress 84
Pak Choy 60
Spinach 56
Cauliflower 46
Cabbage 32
Lettuce 28
Chinese Mustard Green (Choy Sum) 25

Vitamin C content in fruits

Fruit(100g) Vitamin C (mg)
Black Currant (about 15 pieces) 200
Guava 184
Kiwi fruit 75
Papaya 62
Orange 53
Lemon 53
Grapefruit 34
Mango 28
Apple 6

Excessive Intake

Although vitamin C has many benefits to our health, excessive dosage (e.g. 2000 - 5000 mg per day) will have negative effects, like diarrhea, burning sensation during urination, formation of kidney stones etc. Remember, the United States RDA suggests a daily intake of 60 mg of vitamin C per day, and research suggests 250 mg is needed to obtain antioxidant effects.

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