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Vitamins are classified as either fat soluble (vitamins A, D, E and K) or water soluble (vitamins B and C). This difference between the two groups is very important. It determines how each vitamin acts within the body.
The fat soluble vitamins are soluble in lipids (fats). These vitamins are usually absorbed in fat globules (called chylomicrons) that travel through the lymphatic system of the small intestines and into the general blood circulation within the body. These fat soluble vitamins, especially vitamins A and E, are then stored in body tissues.
Fat soluble vitamins, once they have been stored in tissues in the body, tend to remain there. This means that if a person takes in too much of a fat soluble vitamin, over time they can have too much of that vitamin present in their body, a potentially dangerous condition called hypervitaminosis (literally, too much vitamin in the body).
Persons can be also be deficient in the fat soluble vitamins if their fat intake is too low or if their fat absorption is compromised, for example, by certain drugs (that interfere with the absorption of fat from the intestine) or by certain diseases such as cystic fibrosis (in which there is a deficiency of enzymes from the pancreas which similarly interferes with the absorption of fat from the intestine).
There is a difference between the vitamins that are naturally water soluble (such as vitamins B and C) and the "water solubilized" form of a vitamin (such as vitamin E) that is naturally a fat soluble vitamin. This form of vitamin E is "water solubilized" by the addition of certain compounds during a specific manufacturing process. It is hypothesized that this "water solubilized form" of vitamin E is more efficiently absorbed through the intestinal wall into the body.
In sum, to respond to your questions:
- "The difference (if any) between vitamins that are "water soluble" and those that are not" -- There is a big difference between the water soluble vitamins and the fat soluble vitamins and this is absolutely a critical distinction.
- "Specifically Vitamin E" -- Vitamin E is a fat soluble vitamin. Although it can be "water solubilized" in the lab to help its absorption through the intestinal wall, once it is absorbed into the body it would appear to behave as a fat soluble vitamin does.