It is best to obtain your vitamins and minerals, aka micronutrients, from whole, organic foods. This may not give us all that we need though, and supplementation is often required.
Vitamins are referred to as either fat or water soluble. The difference in them is dependent on what solution they dissolve in, i.e. fats/oils, or water.
A, D, E, F, & K are the fat soluble vitamins. Care must be taken with these as they are stored in the body, so this increases the risk for toxicity.
The other category, the water soluble vitamins; are the B-group, C, & P. They cannot be stored in the body. These vitamins are lost through the body through perspiration and urination. Because of this, it is essential for you to replenish these on a daily basis. If this is not done, deficiencies can occur.
You may have heard of the RDA, or Recommended Daily Allowance, that is our standard of daily requirements for vitamins. This system has been in place since the 1940's, and is only based on estimations of what we need. These allowances are also based on the assumption we know all there is as far as vitamins go, and even worse, differ from country to country. They are only requirements in place to help us avoid vitamin deficiencies, the minimum our bodies need.
The somewhat outdated views of this system was proposed to be replaced in 1993. Some refer to it as "The New Paradigm'. This system is called the Dietary Reference Intakes (DRI). Within this are the Adequate Intake Levels (AI), the Estimated Average Requirements (EAR), the Recommended Dietary Allowances (RDA), and the Tolerable Upper Intake Levels (UI). You can learn more about these in further detail by following the link...