When I have a cold or otherwise feeling ill, I like to take vitamin C supplements. I've noticed that they almost invariably have amounts way above the recommended daily allowance.
For example, one that I'm looking at now contains 1000mg, where the RDA is 90mg. That is around 11x more than is needed. I've noticed similar things on other vitamin supplements.
What is the purpose in providing such large doses? This answer for example, suggests that 1000mg of vitamin C can actually be harmful. Why not just provide the RDA?