Is it true that extra vitamins, through supplements and so forth, can shorten people’s lives?

Studies to see if vitamin supplements would reduce deaths from cancer and heart attacks were stopped after a few years because more people in the groups taking the supplements (in particular beta-carotene) were dying than in the groups taking placebo. I’m surprised that companies can still market beta-carotene as a supplement to the general public. If a prescription medicine had had similar trial results, it would have been taken off the market. I see the vitamin makers call the trials ‘fatally flawed’. I don’t see the flaw in the published papers, and would be grateful if someone could point it out to me. In the meantime I’m sceptical about the claims for ‘anti-oxidants’. We get plenty of vitamins from normal food without needing to pop pills.