Not all nutrients required by the body, are synthesized by the body. An example of these are the essential and non-essential amino acids. Essential amino acids are those that are not synthezied and are therefore “essential” in our diet. FYI – You do NOT need to learn the names of the essential or non-essential amino acids.
Vitamins are organic compounds that are required in small amounts in order for effective metabolism. They cannot be synthesized by the body and all have to be obtained through diet. Few foods contain Vitamin D [fatty fish such as salmon and tuna, beef liver, cheese and egg yolks] Vitamin D from these foods is generally in the form of Vitamin D3. This form of Vitamin D is also produced in covered skin through exposure to ultraviolet B radiation. Many foods we eat contain fortified Vitamin D (added Vitamin D). In the 1930’s a milk fortification program was implimented in the United States to combat rickets, which was at the time a major health problem.
And finally, here is a video on ascorbic acid (otherwise known as Vitamin C) and the acknowledgement of Casimir Funk for coining the term vitamin, around 1910. Interesting many mammals can produce there own vitamin C, though this ability has been lost ion primates, guinea pigs and humans
Take a look here.