Well I`ve got a bad cold, and I take Vitamin D every day. The Vitamin D3, or cholecalciferol one that is supposed to prevent a cold or flu. So that`s bullshit too then... I would be better off stroking my magic native American healing wand!
I don't know about anything preventing a cold/flu, but I discovered as soon as I start to feel a cold coming on I just gargle -
"Listerine Mouthwash". (needs to be the original). I think the throat is the main source where the cold virus resides.
If you concentrate your fight against them in that area, you will feel much better and recover sooner.
Need to gargle regularly though (and sip a little down each time) as the virus does try to build up its forces and have another go at you.
Think of the virus as an army of soldiers, if you keep on destroying them using this proven method of mine, there will be eventually no soldiers left to fight you.
This is the only way that I have discovered on how to beat the cold/flu.