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Fat Soluble Vitamins vs Water Soluble Vitamins


Updated July 02, 2014

Question: Fat Soluble Vitamins vs Water Soluble Vitamins

What’s the difference between fat soluble and water soluble vitamins, and what is its significance for people with cystic fibrosis?


Vitamins are classified as either water soluble or fat soluble based on how they are absorbed and used by the body.

Water soluble (Vitamin C and all of the B vitamins): Water soluble vitamins are vitamins that our bodies do not store. These vitamins dissolve in water when they are ingested, then go in to the blood stream. The body keeps what it needs at that time, and excess amounts are excreted in the urine. Since they can’t be stored, everybody needs a continuous supply of water soluble vitamins in order to stay healthy.

Fat Soluble (Vitamins A, D, E and K): Fat soluble vitamins are those that are normally stored in the body. When these vitamins are ingested, they dissolve in fat. In a person with a healthy digestive system, the body uses what it needs at that time and stores the rest for future use. Since people with cystic fibrosis often have pancreatic insufficiency and do not digest or store fats properly, the excess is not stored but excreted in the stool. Due to this, people with cystic fibrosis need a continuous supply of fat soluble vitamins just as they do with water soluble vitamins.

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