Most animals and plants are able to synthesize their own vitamin C. This is done through a biochemical pathway that depends on 4 key enzymes which convert glucose to vitamin C. In mammals, the glucose is extracted from stored sugar (glycogen) and the transformation into vitamin C is produced in the liver.
Vitamin C Metabolism
Humans lack the L-gulonolactone oxidase enzyme that is critical for the last step of vitamin C synthesis. Humans require a good amount of vitamin C in order to build healthy tissue collagen and promote strong immune function. When low levels of vitamin C are present the body makes due by recycling the oxidized version of vitamin C. This redox cycling is performed by the master anti-oxidant glutathione. As long as enough glutathione is present the vitamin C redox cycle can continue.
The Nobel prize winning chemist Linus Pauling discovered that white blood cells need very high doses of vitamin C in order to function effectively. In the late 1960's, he developed the understanding of using high dose vitamin C to combat the common cold. This technique has worked effectively for many individuals; however, there is more to the story when it comes to vitamin C.
The Glucose/Vitamin C Competition
In the 1970's, Dr. John Ely discovered the Glucose-Ascorbate-Antagonism (GAA) theory. Glucose and vitamin C (ascorbate) have a very similar chemical makeup. This theory proposes that elevated glucose levels compete and effectively restrict vitamin C from entering cells. Both glucose and vitamin C depend upon the pancreatic hormone insulin and its signaling effects in order to get into cells.
There is an important receptor called the Glut-1 receptor that activates in response to insulin to allow both glucose and vitamin C to enter the cell. However, glucose has a greater affinity for the insulin receptor. This means that the greater the content of circulating blood sugar the less vitamin C will enter the cell.
White Blood Cells Need Vitamin C
White blood cells have more insulin pumps than any other type of cell and may contain 20 times the amount of vitamin C as other cells. They also need 50 times more vitamin C inside the cell than in the blood plasma in order to handle the oxidative stress that occurs when they encounter a pathogenic substance.
When white blood cells encounter pathogenic bacteria and viruses they must ingest or phagocytize these organisms in order to neutralize them. The phagocytic index measures how effective a particular white blood cell is at destroying viruses, bacteria & cancer cells. Elevated blood sugar impairs this phagocytic index. In fact, a blood sugar of 120 reduces the phagocytic index by 75%.
HMP Shunt Dynamics
Glucose and ascorbic acid also work on the hexose monophosphate (HMP) shunt. The HMP is a biochemical pathway that produces NADPH. White blood cells need NADPH to create superoxide and other reactive oxygen species that oxidize and destroy pathogens. Vitamin C not only helps produce NADPH but also regulates quantities so the white blood cell does not create too much oxidative stress in its attempt to protect the body.
Vitamin C activates this important shunt while glucose inhibits it. This HMP shunt also produces ribose and deoxyribose which provide important raw materials for the formation of new white blood cell RNA/DNA. When the immune system is under attack it needs to quickly produce new immune cells. If blood sugar is high enough to turn off the HMP shunt it will reduce the quantity of RNA/DNA and the amount of new immune cells formed.
Important Immune Boosting Steps to Consider:
1) Never take synthetic vitamin C and especially not in a sweetened candy or drink form
2) Use whole food sourced Vitamin C supplements
3) Use low sugar whole food forms of vitamin C such as lemon, lime, & green veggies as much as possible.