When examining a diet we have probably all wondered why health officials include statements like "get enough vitamin C" and encourage well-rounded nutrients. The fact is, our bodies are incapable of storing certain vitamins, such as the B complex and vitamin C. These vitamins have to be replenished daily, whereas the ones stored in fat -- A, D, E and K -- are readily available when we need them.
Fat Storage
It would be nice if the human body stored water as opposed to fat. Only camels and plants can store water, the human body cannot. All the liquids consumed daily are absorbed within the intestines and circulated throughout the body. Vitamins that are water-soluble, such as vitamin C and the B complex, float in the bloodstream and are deposited where necessary. The remainder of unused vitamins will flush out in urine. The fat-soluble vitamins A, D, E and K are digested and used in a similar fashion, except the excess of these vitamins are stored in the liver and fatty tissues.
Solubility
The vitamin groups are named fat-soluble and water-soluble for a good reason. Fat-soluble vitamins require the presence of fat for digestion. Once these vitamins are submerged in a layer of fat, the liver, pancreas and gallbladder work together releasing enzymes to digest them. This is the same reason why people who use fat-sparing diet pills may need extra supplements -- the diet pills flush out the fat-soluble vitamins with the fats. Conversely, water-soluble vitamins only need water to break down and be absorbed in the small intestine. They are not as complex in structure and are quickly used and discarded.
Balance
The body is constantly striving to maintain a perfect balance. Vitamins help regulate energy and metabolism as well as provide a catalyst for all human functions. Too many vitamins are just as dangerous as too little as both can lead to health problems. The average human could consume many calories daily without actually taking in any vitamins or nutrients. The water-soluble vitamins must be replenished daily through foods or supplements. Conversely, if someone does not get enough fat-soluble vitamins they will be released from fatty tissues when the body senses an imbalance. Eventually those storage depots are depleted and malnutrition diseases ensue.
What They Do
The system by which the body signals deficiencies and releases vitamins is complex. Although the human body knows what to do with vitamins once we consume them, it cannot tell you which ones it needs until deficiencies are severe. This is the main reason a healthy, well-balanced diet is the best bet for health. Although some vitamins are stored and some are not, the body needs the full complement to function at top efficiency. Once absorbed, the vitamins have many different functions throughout the body including keeping the immune and cardiovascular systems healthy, the bones strong and metabolism regulated.
References
- "Human Diseases", 2nd Ed.; M. Neighbors & R. Tannenhill-Jones; 2006
- Kids Health: Vitamins
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