There are three different types of vitamins; synthetic, natural altered and natural unaltered. Click here to read that post explaining the difference. Of the three, only natural UNaltered can be utilized by the body.
The next post explains the single most important factor in choosing a vitamin -- is it alive or dead? You need life to create life. The con job is that you can swallow synthetic vitamins (many of them are labeled NATURAL) whose source is petroleum or coal tar and build health. It is NOT possible. How can you tell the difference? How can you know if the product you are taking is GMO free? There are a couple tests you can do to help determine if your vitamins can be assimilated by your body. Read that post here.