Many people take vitamin supplements daily to complement their diet. Ascorbic acid, also known as vitamin C cannot be manufactured by humans so must be included in the diet. Other mammals can make it themselves.
This vitamin is essential in our diets. If we do not eat enough fruit and vegetables, or take supplements, the disease scurvy results, as experienced by sailors in the past. The symptoms of scurvy are teeth falling out, blisters and sores. These are a result of the body being unable to make collagen, which requires vitamin C.
Vitamin C is also an antioxidant, scavenging for rogue free radicals and thus protecting us from cancer. It is believed that a large intake protects us from the common cold, but this has not been proved.
Compounds known as Michael acceptors are potentially dangerous to living organisms. This is because they undergo conjugate addition:
By this mechanism, Michael acceptors attack enzymes, particularly DNA polymerase, which is vital in DNA replication.
Any compound that is good at conjugate addition is probably toxic and carcinogenic. Most Michael acceptors damage the DNA replication process unselectively. However, we are protected from this by glutathione, a compound present in most tissues:
Glutathione is a tripeptide. The thiol (SH) group of glutathione scavanges carcinogenic compounds by conjugate addition:
If glutathione, which is naturally abundant in the body, is removed by oxidation and can no longer scavenge toxins, then the organism is in danger. Vitamin C removes stray oxidising agents therefore protecting the supply of glutathione. This is one reason why vitamin C is so beneficial to humans.