I've been self medicating for 30+ years. I take vitamins and herbal supplements. I think it helps my over all health. Even if you're not a nutcase like myself it's important to remember that #1 The RDA levels on vitamins are probably much too low. #2 Even if you eat healthy, you cannot get all the necessary nutrition from the "American" diet.
On a recent 9 hr trip I listened to a CD by the guy that ate at Mac D's for a month. He gives some scary info on our typical fast food frenzy.

I was never a fast food addict but I did stop for a quick burger or my favorite, a jamoca shake from Arby's. Now I can't do it.
The nutrition advice is to shop the perimeter of the grocery store and stay away from anything in a box. Easy to say if you don't work 40 hours +5 hours for lunch,18 mile round trip to work.....it's all about time!!!!!
If you read the ingredient panel you end up putting it back on the shelf.
The worst offender is high fructose corn syrup. I already knew it was the bad dude but the CD gave lots more data on the evils of hfcs. Don't eat it!!