Oh, one more quick note about multivitamins. They generally do not work as they are intended, which is part of the reason that the nutrition received naturally through one's diet is so much so emphasized these days, so it's no wonder that your son stopped taking one; it probably didn't help him.
But, in general, vitamins are something of a ruse for everyone, not just your son. In fact, not long ago I was reading in the Times about another recent study which served to disprove the effectiveness of vitamins. It showed how certain populations which take vitamins show no overall health benefits by doing so. Acknowledging the ineffectiveness of the "once-daily" muti-vitamin, Dr. Oz, for example, advises that your multi-vitamin be broken in half and taken at two different times of the day. Even Dr. Oz's good-intentioned claim however seems questionable however.
At any rate, every doctor will agree to the benefits of limiting dietary supplements to a minimum, for example only taking a vitamin d, vitamin b, or calcium supplement, and receiving the majority of ones nutrition through plain ol' food (preferably with limited processing). Just an additional thought after re-reading your post. Sorry for the long-windedness.