i wish i had time to find and link it for you before i head to work, but i read a study that tested common cold remedies like vitamin C to see how well they actually hold up and how much is just in our heads.
taking extra vitamin C makes no difference, as your body does not do anything with the extra except get rid of it. it can only absorb so much in a day.
they had a few other things like garlic and cold FX which performed the same, mostly a placebo effect. (not to say its not healthy, just that taking extra made no difference on cold length)
i dont remember exactly what all was on the list, but the one thing i do remember is that the ONLY home remedy that actually reduced the length of colds in the test group by any significant margin was Echinacea (sp?). it boosts your immune system a great deal and helps you fight off the cold a lot faster.
my daily vitamin cocktail includes vitamin D, vitamin C, a multi-vitamin, cod liver oil, garlic pills, and echinacea. When i feel a cold coming on, i double my daily dose of garlic and echinacea and the cold symptoms are usually gone within a day or two. i've handed out baggies of it to friends at work to try when they are sick with the same effect. its the number one cold remedy in my experience.