Vitamin C also known as ascorbic acid, is a water-soluble vitamin. As humans we are unable to synthesize it due to lack of the last enzyme in the vitamin C synthetic pathway, gulonolactone oxidase. Our bodies are able to store only a certain amount, therefore ascorbic acid should be consumed on a daily basis to avoid deficiency. Vitamin C has many functions in our bodies, including synthesis of collagen, carnitine, tyrosine (also its catabolism) and neurotransmitter. The role of vitamin C in these reactions is to function as a cofactor to maintain the iron and copper atoms in the metalloenzymes in the reduced state. In addition Vitamin C is an important antioxidant. Other functions include possible effect on certain disease have been proposed but the research is inconclusive. These diseases include common cold, it is thought that vitamin C may enhance immune cells while also destroy histamine, which causes many of a cold’s symptoms. These effects have been refuted by some investigators. High intake of vitamin C has been investigated in relation to a protective effect against cancer especially oral cavity, pharynx, esophagus, and stomach. Some researchers have shown the prolonged survival time in cancer patients, while others didn’t show any benefits. Increased vitamin C plasma concentrations has been linked to decreased risk of heart disease, thus lower blood pressure, while low status was related to higher blood total cholesterol. Again the research is mixed. Poor status of vitamins C and E as antioxidants has been associated in some studies with the development of cataracts.
Severe vitamin C deficiency leads to scurvy. It is a condition with many different signs and symptoms including bleeding gums, small skin discolorations due to ruptured small vessels sublingual hemorrhages, easy bruising, impaired wound and fracture healing, joint pain, loose and decaying teeth, and hyperkeratosis of hair follicles. Scurvy can be easily remembered by the four Hs – hemorrhagic signs, hyperkeratosis of hair follicles, hypochondriasis, and hematologic abnormalities.
Even though vitamin C is water-soluble it can become toxic because its absorption is saturable and dose dependent. It is more likely to become toxic if taken in several large doses (>1 g) throughout the day than with ingestion of the same amount as one single dose. Level of 2 g of vitamin C has been recommended as tolerable upper intake. Most common side effects include abdominal pain and osmotic diarrhea. Other signs in adults that may appear include nausea, vomiting, flushing of the face, headache, fatigue and disturbed sleep. Some research show the increased risk for development of kidney stones (because vitamin C is metabolized to oxalate, a common constituent of kidney stones) and iron toxicity in those with renal disease and disorders of iron metabolism, respectively. Because vitamin C enhances iron absorption its excess can create a problem for people with iron overload disorders like haemochromatosis. Large doses of ascorbic acid may also be dangerous during the first few weeks of pregnancy, as it may suppress the production of progesterone from the corpus luteum. Progesterone is crucial for the maintenance of pregnancy, if its production is blocked, early miscarriage may be an end result.
Best sources of vitamin C include asparagus, papaya, oranges, orange and grapefruit juice, cantaloupe, cauliflower, broccoli, Brussels sprouts, green peppers, grapefruit, kale, strawberries and lemons. The RDA for adult male is 90 mg, while for female is 75 mg. and no more than 2 grams per day (2000 milligrams per day).