There are plenty of benefits to vitamin C but, for most people, preventing colds is not one of them.
I've done a lot of reading on the subject over the last few years, as we get older it gets more and more important to use every possible method to keep ourselves healthy (I speak from the over 60 crowd).
When I first ran across Dr. Pauling's work, I was skeptical, but decided to get it a try (can't hurt, can it?) To this day I still do not regret the decision.
There have been a lot of studies performed over the years, most were limited to the use of a very small amount of Vitamin C (USDA values), some with larger doses but only a few days prior to the introduction of a cold virus. I can say with real confidence that I have not had a single cold with the usual high fever, runny nose, etc. in the last few years.
I was exposed to an office worker this spring while he suffered with two colds (of about two weeks each) and only had a very mild reaction. Vitamin C? Maybe, maybe not, but it doesn't hurt.
In all fairness, there are also studies that do find that colds are less intense and shorter after taking Vitamin C.
Does Vitamin C Prevent Colds?
PLoS Medicine - Vitamin C for Preventing and Treating the Common Cold
etc. etc. etc.
I'm not doctor, but I do feel that taking any vitamin requires time for the body to react and adopt. That's why a short term study where those in the test who had only been given Vitamin C for just a few days prior did not have impressive results. Those tested who had been taking Vitamin C over a long period of time did show better results (Dr. Pauling research for example).
Actually it was my doctor that suggested I look into taking more Vitamin C based on some research he had done for himself. He's now retired four years, in his mid 80's and still runs 5 miles a day, winter and summer. (I couldn't go 1/4 mile feet if I want to.) God bless the old country doctors that really believed in the Hippocratic oath rather than the ol' mighty dollar.
And there's also evidence that Vitamin C can prevent cancer.
Antioxidants and Cancer Prevention: Fact Sheet - National Cancer Institute
Zinc is another good supplement to take when you feel a cold coming on. Like Vitamin C it will not prevent a cold, just strengthen the immune system and shorten its effects.
I also like a product called Airborne. My wife and I take it whenever we feel like we're getting a bug. Gives about three hours of relief.
I liked your remarks on Vitamin D. I remember Reader's Digest had an article on it last year (year before? - isn't memory the second thing to go). It recommended we increase to dosage to 800 mg (and in some cases 1200 mg). I decided because of that article to increase my dosage to 800 mg and never had any negative side effects.
Perhaps we could all take a tip from a couple of unrelated professions.
The first, the fella who cleans out my septic tank, claims he hasn't had a cold or flu since he started working for the company (ten years at that time). He felt that being constantly exposed to some of the most deadly bacteria every day has strengthened his immune system to the point where no germs could survive [sic]. Makes an interesting point however.
The second is workers in nursing homes. They are constantly exposed to all kinds bugs. My aunt was in the the local home my wife visited daily and got to know the staff very closely. They told her to use disinfecting hand cleanser whenever she she came in. They also told her to take a daily vitamin pill and to wear a face make when the outbreaks became severe. She did catch a bug once, but the whole place was going through an epidemic and I doubt anyone could have avoided catching it.
For myself, I'm still going to stick with higher amounts of Vitamins B, C, D, E and beta carotene. It works for me.
Take care,
Dennis
