This is one of my comments from a discussion on LinkedIn Group Fitness and Wellness Professionals. I can add to it but won't for now.
Insiders like pharmacists or doctors can cite more studies, probably on either side. I won't spend a lot more time on this. The supplement biz is a biz just like pharma is. There are "good and bad" people everywhere. Some pharma companies have really smart people turning out drugs that save lives. And some drugs have may side effects that can harm or kill. And some people that don't need to take them take them, when more can learn about the mind-body connection, meditating, etc. Some people try to get away with things like working around regulation. [Again, if pharma people do it, supplement ones can too.] You can see two sides in almost anything. For the most part, I'd bet that unless one is sick, pregnant, old, going through extreme training or competition, etc., a daily good diet will take care of what they need. Many vitamins and minerals are water-soluble, which means you get rid of them in the bathroom, and high amounts of the fat-soluble ones are not good.
A good resource is www.pubmed.gov. Here are two articles. There are more that can be found on "both sides" I am sure. http://www.ncbi.nlm.nih.gov/pubmed/15229713
http://www.ncbi.nlm.nih.gov/pubmed/15035689 ("not enough studies")
http://www.ncbi.nlm.nih.gov/pubmed/19960886 (supplements alter chemistry; deaths found)
Disclaimer: None of the above information can be taken as a substitute for advice from a medical professional such as a physician.
My third book, Pocket Guide to Fitness, is available on www.louizapatsis.com, http://www.authorhouse.com, www.bn.com and http://www.amazon.com. If you look up my name on those Web sites, you will find my other books The Boy in a Wheelchair and Life, Work and Play: Poems and Short Stories.