Tuesday, March 16, 2010

Vitamins: Fat Soluble Versus Water Soluble

Vitamins are organic substances that our body can’t manufacture. This means they must be consumed in the diet. 13 different vitamins have been isolated and classified. In general, we put them into two categories: fat-soluble or water-soluble. One of the key concepts in vitamin nutrition is bioavailability. Bioavailability is the actual amount of the nutrient that you absorb and can utilize. If a book says some food has 60 milligrams of folic acid, that’s what is in the food, not necessarily what you can get out of the food.

There are some factors that influence bioavailability. First, the form of the vitamin. In the example of vitamin E, it has eight different forms and are not all equally effective. There is also the difference between natural or synthetic vitamins. Most of the time vitamins from food are better. In the case of folic acid, its synthetic form is more biologically available.

Sometimes a food component can increase or decrease bioavailability. Folic acid is better absorbed on an empty stomach than with food. In fact, synthetic folic acid on an empty stomach has a bioavailability of almost 100%. When taken with a mixed meal, the bioavailability goes down to about 85%.


Fat-soluble vitamins are the ones which dissolve and remain in the body’s fat stores. For example, if you have excess body fat, vitamin D is held in the fat, making it less available to other tissues within the body. Because they are fat-soluble you can store them in your fat. There is a less urgent need to have them on a daily basis.

As a group of vitamins, fat soluble include vitamins A, D, E and K. They should not be consumed in excess without medical advice.

Toxic reactions can occur with large quantities of these fat soluble vitamins. The most notable case is with vitamin A.


Water soluble vitamins are the ones you need to consume on a daily basis because they are lost in your urine. This doesn’t mean that you can’t have an undesirable side effect with excessive intake. These vitamins act as coenzymes: small molecules that combine with a larger compound to form an active enzyme. In other words, they accelerate chemical reactions within the body.

Within the category of water-soluble we have vitamins C, B1 (thiamin), B2 (riboflavim) , B6 (pyridoxine), niacin, pantothenic acid, biotin, folic acid and B12. If your diet contains less than 50% of the recommended values, deficiencies can begin to show up within 4 weeks. The excess of water-soluble vitamins is voided by urination. Vitamin B6 is a water-soluble vitamin that can have a toxic effect.

Water-soluble vitamins are dispersed in body fluids and aren’t stored to any great extent. The exception is vitamin B12. You can actually store vitamin B12 up to 1 or 2 years in your liver.

They exert their greatest influence for about 8 to 14 hours after ingestion. After that, their potency decreases.

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