Vitamin C

Without the vitamin C available from eating fruit and vegetables, we could not survive.

Although isolated in the 1930s, it was a team of New Zealand scientists working at Plant & Food Research in Auckland in 2006 (published May 2007) who discovered the missing link in our understanding of how it is produced in plants.

History of vitamin C

An early description of the vitamin C deficiency disease known as scurvy is in the log of an expedition led by Frenchman Jacques Cartier to Quebec, Canada, in the summer of 1535.

By early November, his fleet of 3 ships became icebound. Without access to fresh food and feeding only on meagre rations, all but a few of the 110 men became unwell. They suffered severe fatigue, inflamed and swollen legs, bleeding gums and rotting teeth. The native Indians of the area advised him to make a brew from the bark and leaves of a local tree and drink small amounts each day until the symptoms disappeared. Cartier’s men regained their health and survived the winter before sailing back to France.

In 1747, British Royal Navy surgeon James Lind set about finding a cure for scurvy, a disease that killed thousands of sailors annually. He discovered that: “... oranges and lemons were the most effectual remedies for this distemper at sea”.

It took the British Navy 50 years to finally bring in compulsory lemon juice rations for all crews. The term ‘limey’ is an old slang nickname for the British and, in particular, sailors.

It was not until the early 1930s that the chemical known as ‘hexuronic acid’, isolated from orange juice and cabbage juice, was acknowledged as the ingredient needed to prevent scurvy. It was renamed ascorbic acid and is known nutritionally as vitamin C.

Production of vitamin C

Vitamin C was the first vitamin to be discovered, the first to be structurally determined and the first to be made artificially.

Industrially, vitamin C is produced from glucose using an unusual blend of biological and organic chemistry. It is a 5-step process with one of the steps making use of a microorganism to make the chemical change.

Vitamin C occurs widely in plant tissues, and most mammals can produce it in the liver using glucose as the starting material – adult goats produce a massive 10–15g of vitamin C per day. Humans and other primates along with guinea pigs and fruit bats are incapable of making their own vitamin C – this crucial micronutrient now has to be supplied through the foods we eat.

It was not until May 2007 that scientists finally reported the missing step as to how plants produce vitamin C. The breakthrough came from a team of New Zealand scientists working at Plant & Food Research in Auckland. Working with various kiwifruit varieties, coupled with the world’s largest kiwifruit DNA database, the team isolated the last undiscovered enzyme in the vitamin C production pathway – an important control point of vitamin C production in plants.

Functions of vitamin C

In plants, vitamin C plays a protective role in the photosynthetic process by acting as an antioxidant, and it is required for the function of a wide variety of enzymes such as those involved in the fruit ripening process. Vitamin C is also crucial for correct folding and secretion of many proteins – a function that it also has in animals.

In humans, vitamin C has a variety of functions, some of which are not yet fully understood. Vitamin C plays a vital role in the production of collagen, which is the principal connective tissue protein found in tendons, arteriesbone, skin and muscle. In scurvy, new connective tissue cannot be formed in sufficient amounts to keep up with the body’s replacement and repair demands. This results in bleeding gums, the loosening of teeth, slow wound healing, anaemia and arrested skeletal development in children.

Some of the other processes that involve vitamin C are:

• the production of chemicals that allow nerves to function effectively
• cellular energy release and muscle function
• the production of several hormones
• the production of bile acids in the liver
• the uptake of dietary iron from the small intestine
• the correct turnover of white blood cells.

How much vitamin C?

Fruits and vegetables have varying amounts of vitamin C that can meet the daily requirement when consumed. Fresh raw meat and liver is rich in vitamin C but needs to be consumed raw, since prolonged cooking converts it into an inactive form.

The amount of vitamin C needed to prevent scurvy is about 10mg per day for an adult. The recommended nutrient intake takes account of this basic minimum but also includes sufficient to maintain a body pool of the vitamin. In New Zealand, the recommended nutrient intake for children and teenagers is 40mg per day and 45mg per day for adults. Two medium sized tomatoes would supply about 40mg, whereas one kiwifruit would supply over 60mg.

Taking vitamin C supplements has been linked to prevention of the common cold but clinical evidence indicates that vitamin C supplementation does not reduce the incidence of the common cold. However, there is some evidence to show a slight decrease in the duration and severity of the symptoms.