Recommended Nutrient Intakes for Vitamin and Minerals

Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin.

Functions

Vitamin C helps specific enzymes and functions as an antioxidant.

Functions include:

• Synthesis of collagen (the principal connective tissue found in tendons, arteries, bone, skin and muscle)
• Synthesis of noradrenaline which is an important neurotransmitter produced in neural tissues
• Synthesis of carnitine which plays and essential role in the transport of fatty acids into the mitochondria where they are oxidised
• Activation of neuropeptides
• Vitamin C is required for the catabolism of tyrosine
• Synthesis of bile acids
•  Increases absorption of non-haeme iron
• Antioxidant - An antioxidant is a substance that prevents the oxidation of another substance caused by free radicals. In cells and body fluids, vitamin C helps to prevent damage to tissues which may be important in preventing disease.

Beyond a level of 200mg/d, virtually all the excess vitamin C will be excreted in the urine within 24 hours.

Cigarette smokers tend to have lower levels of vitamin in the blood. This seems to be partly due to lower intakes of vitamin C, but studies have shown that the metabolic turnover of Vitamin C in smokers is twice that of non-smokers. This means that a smoker needs significantly more dietary vitamin C to maintain a body pool of vitamin C equivalent to that of non-smokers. In times of stress such as infections, wound healing and exposure to cold, may increase the need for vitamin C.

Recommended Intakes

Table 8: Recommended Intakes for Vitamin C (mg/day)

Food Sources

Fruits and vegetables are major sources of vitamin C in the diet. Together they contribute about 90% of the vitamin intake in New Zealand.

Some examples of sources of vitamin C include blackcurrants (200mg/100g), kiwi fruit (120mg/100g), cauliflower (60mg/100g) broccoli (58mg/100g), oranges (50mg/100g), strawberries (46mg/100g), spinach (31mg/100g). Potatoes contain 10mg of vitamin per 100g, but may provide a significant amount of vitamin C in the diets of some people because of the high amount of potatoes eaten.

Deficiency

Scurvy is the disease that results from a deficiency of vitamin C. Scurvy is uncommon in populations unless there is a prolonged shortage of fruits and vegetables.

Symptoms of vitamin C deficiency include weakness, fatigue, inflamed and bleeding gums, impaired wound healing because scar tissue will not form, skin haemorrhages and depression. Atherosclerotic plaques grow rapidly in the arteries. Bone rebuilding is also decreased and the ends of long bones become softened, malformed and painful, with fractures appearing. The teeth become loose as the cartilage around them weakens. Sudden death may occur, caused by severe atherosclerosis or by massive bleeding into the joints and body cavities.

 The symptoms usually occur when blood vitamin C levels fall below 2mg/L (normal blood vitamin C levels range from 4-15mg/L). The total body pool of vitamin C plateaus at about 1500mg. Deficiency symptoms occur when the body pool of vitamin C falls below 300mg. Full recovery from the clinical manifestations of scurvy requires as little as 10mg of vitamin C per day.

Toxicity

The toxicity of vitamin C is low. Some toxic effects have been reported including nausea, abdominal cramps and diarrhoea.

Large amounts of ingested vitamin C have been reported to have interfered with medical regimes. Large amounts of vitamin C excreted in the urine obscure the results of tests known to detect diabetes. People taking anticlotting medications may abolish the effect if it is also taken with large doses of vitamin C. Vitamin C supplements are also dangerous for those people with iron overload as vitamin C enhances the absorption of iron. Those susceptible to gout may be more prone to developing kidney stones if they take large doses of vitamin C.

The range of safe intake seems to be broad. From a minimum of 10mg/day to about 300mg/day appears safe. People who venture outside these limits may be taking health risks.

Vitamin C and the Common Cold