Vitamin C is a water soluble vitamin so we must consume it on a regular basis because excess is excreted in the urine. Most animals can make their own vitamin C from glucose. Humans and guinea pigs are two groups that can’t synthesize their own vitamin C, so we must consume it in our diets.
Vitamin C is most well known for its role in preventing scurvy which is a disease that sailors got on long sea voyages centuries ago. Scurvy was characterized by bleeding tissues especially the gums, and is thought to have caused more than half of the deaths that occurred at sea.
One reason why vitamin C prevents scurvy is that it assists in the synthesis of collagen. Collagen is a protein that’s critical component of all connective tissues in the body including bone, teeth, skin and blood vessels. Collagen assists in preventing bruises and it ensures wound healing. Without adequate vitamin C in the diet, the body can’t form collagen and tissue hemorrhage or bleeding occurs. Vitamin C may also be involved in the synthesis of other components of connective tissues.
Vitamin C is also involved in the synthesis of DNA, bile, neurotransmitters, and carnitine which transports long chain fatty acids from the cytosol into the mitochondria for energy production. Vitamin C also helps to ensure the appropriate levels of thyroxine are produced to support basal metabolic rate and to maintain body temperature. Other hormones that are synthesized with assistance from vitamin C include epinephrine, nonepinephrine and steroid hormones.
Vitamin C is also an antioxidant. Like vitamin E, it donates electrons to free radicals to prevent damage of cells and tissues. It also protects LDL cholesterol from oxidation which may reduce the risk of cardiovascular disease. Vitamin C also acts an important antioxidant in the lungs to protect us from damage caused by the ozone and cigarette smoke. It enhances immune function by protecting the white blood cells from oxidative damage that occurs in response to fighting illness and infection. In the stomach, vitamin C reduces the formation of nitrosamines which are a cancer-causing agent found in foods like cured or processed meats.
Vitamin C also regenerates vitamin E after it’s been oxidized. The regenerated vitamin E can continue to protect cell membranes and other tissues. Vitamin C also enhances the absorption of iron. It’s recommended that people with low iron stores should consume vitamin C rich foods along with iron sources to improve absorption.
The RDA for vitamin C is 90 mg per day for men and 75 mg for women. The RDA for smokers is 35 mg more per day than nonsmokers. Other situations that may increase the need for vitamin C include healing from a traumatic injury, surgery, or burns and the use of oral contraceptives among women.
Fruits and vegetables are the best sources of vitamin C. Because heat and oxygen destroy vitamin C, fresh sources have the highest content. Cooking foods also leaches their vitamin C which is then lost when straining them. Citrus fruits, potatoes, strawberries, tomatoes, kiwi fruit, broccoli, spinach, cabbage, green and red peppers and cauliflower are excellent sources of vitamin C. Fortified beverages and cereals are also good sources. Dairy foods, meats, and nonfortified cereals and grains provide little or no vitamin C. By eating the recommended amount of vegetables and fruits a day, the body will meet the required amount of vitamin C.
Because vitamin C is water soluble, we usually excrete any excess. Consuming excess food sources doesn’t lead to a toxicity, only supplements can. Taking megadoses of vitamin C is not fatally harmful but side effects exceeding 2,000 mg a day can include nausea, diarrhea, nosebleeds, and abdominal cramps.
Vitamin C deficiencies are rare in developed countries but can occur in developing countries. The symptoms of scurvy occur after about 1 month of a vitamin C deficient diet. Anemia can also result from a vitamin C deficiency. People most at risk are those who eat few fruits and vegetables and those who abuse alcohol and drugs.
Source: Thompson, Janice, Melinda Manore, and Linda A. Vaughan. The Science of Nutrition. San Francisco, CA: Pearson Benjamin Cummings, 2011. Print.