Vitamin C – a first introduction
Vitamin C (also known as ascorbic acid) is a water-soluble vitamin that, in addition to its function as an electron donor (or antioxidant), also functions as a coenzyme for many other enzymes.
Humans have lost the ability, through evolution and through mutation, to make “ascorbate” (yet another name for vitamin C) in their body.
Most of the other animals and plants can still do this.
What does Vitamin C do ?
Vitamin C is a vitamin involved in many chemical reactions in the body.
It’s responsible for the production and strengthening of the collagen matrix and maintains connective tissue cells  such as skin, bones, muscles, joints and tendons.
Furthermore, vitamin C maintains the blood vessels and keeps them flexible and elastic .
It helps maintain a healthy heart , can reduce blood levels  and supports the immune system in curing diseases or injuries .
Vitamin C is also the main raw material for the production of our “master antioxidant” glutathione in the liver .
It also helps to eliminate heavy metals, such as lead and mercury, from the body  .
Vitamin C interacts with Vitamin E, a fat-soluble vitamin that sits around the surface of our cell membranes, and is sometimes referred to as Vitamin E’s sister because both work together to maintain the cells .
Vitamin C also prevents the conversion of nitrates and nitrites into harmful nitrosamines in the intestinal tract. Those nitrates and nitrites  are used to keep meat pink or are naturally present in large amounts in celery (> 250mg / 100g!)
How is vitamin C absorbed?
In the small intestine, there are small tentacles that absorb nutrients. These tentacles are also called “villi” and absorb both the reduced form of vitamin C (ascorbic acid) and its oxidized form (dehydroascorbic acid).
These villi absorb the vitamin C piece by piece until a certain saturation point is reached and the absorption proces is stopped for a certain time.
The unabsorbed vitamin C continues through the large intestine and leaves the body.
Vitamin C absorption within different cells is extremely different.
The brain and white blood cells are saturated much faster than eg the heart.
An interesting observation can also be made during transport.
Ascorbic acid is transported by the “Sodium-Vitamin C Co-Transporters” SVCT1 and SVCT2.
Dehydroascorbic acid, on the other hand, is very similar to the glucose molecule and an antagonist of it. They both use the same transporters, namely the GLUT transporters, and compete with each other to be transported by it  .
Thus, dehydroascorbic acid cannot use the SVTC transporters.
When one eats a carbohydrate-rich meal, such as pasta, potatoes, etc., there is a high insulin response due to the large amount of glucose in the blood. Glucose, as mentioned, uses GLUT transporters to get to the cells.
Due to that large amount of glucose, vitamin C (in the form of dehydroascorbine) no longer has the ability to use the GLUT transporters, making it much more difficult to absorb vitamin C.
People with low glucose levels in their blood can therefore absorb vitamin C more efficiently because more GLUT transporters are available.
Is vitamin C recycled?
Our kidneys constantly purify and filter our blood.
They do this via nephrons, of which each kidney contains a million.
Nephrons, in turn, contain a “glomerulus”, the part of the nephron responsible for filtering the blood, making urine and removing unnecessary and harmful substances.
Within the nephron, other cells are responsible for the reabsorption of Vitamin C. When saturated with vitamin C, they leave the body through urine .
This process starts when your plasma level is between 50 – 60 µmol / dl.