Vitamins are not needed by everyone equally. We all differ in how we metabolize things, and some people need more of one thing than another...this is genetically driven.

Some vitamins we consume are not ACTIVE yet for the body to use. If some genetic error exists you inherited, you cannot utilize some after you absorb them. They float around in the blood until eliminated and will show up on testing and that will be deceiving because they are actually not working.

Folic acid and B12 have to be activated (methylated) to work. If the enzyme is missing or not in great enough amounts, then you will be deficient even though you are taking them in some form.
This is called MTHFR polymorphism and there is a DNA test for it now. It is estimated that 10-30% have this error.

Some people cannot metabolize alcohol normally, because of faulty B1 genetics:
http://www.uic.edu/classes/phar/phar...se_report3.htm
Some people of Asian ancestry today cannot metabolize alcohol properly because of the enzyme needed is in short supply or not there and are intolerant when consuming ethanol:
http://en.wikipedia.org/wiki/Alcohol_tolerance