A bit more.
way to establish whether vitamins actually do anything other than lighten your wallet is to do proper science: large scale, double-blind long-term studies.
Those studies are starting to be done and it's bad news for the vitamin industry. Take a look here: Vitamins: Research Shows No Benefit and Some Risks
Again, the Cochrane review is the gold standard:
We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomized trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.
At least one major study was abandoned because the supplemented group were developing significantly greater levels of mortality. I think this was a Boston based study (?) using doctors as partcipants.
As expected, the supplement industry went into default accusations of pharma-funding, yadda yadda, which makes no sort of sense where Cochrane is concerned.
The vitamin maketing machine rumbles on, but the science is gradually seeping out. Twenty years from now, multivits for the healthy population will have gone the way of boron, kelp and (hopefully) homeopathy.