My Mom used to always tell me to take a vitamin c supplement when I had a cold. She used to hand me these large pills when she detected a sniffle or when cold season was around. I always felt good feeling that the magic vitamin c was doing something to help me fend off or even overcome my cold. When I was older, living on my own and couldn't afford the $30 bottles of love I would faithfully drink orange juice hoping for the same effect. It seemed that every time I took my C or drank my juice the cold would go away a few days later. I don't remember what happened if I forgot to take the supplement.
In the past few years I have purposely stopped taking vitamin c when i've had a cold, just to see what would happen. Turns out I still get over my colds in the same amount of time, as far as I can tell. Also seems that a scientific consensus has been building and shows that vitamin c has no greater effect than placebos for the common cold (WebMd). In fact large doses can actually cause health problems (slate). Does anyone remember Airborne? Wasn't it invented by some elementary school teacher who claimed her pupils were infecting her constantly and fizzy vitamin c concoctions were a sure fire prevention? Looks like she used fake evidence in a phoney lab to back up her potion's claims (consumerist).
In the end it looks like our own bodies' immune systems do best at miraculously curing ourselves from colds and they don't need any help except for a balanced diet and some exercise. The perceived effects of vitamin c are likely what psychologists call a cognitive determinant of a questionable belief or a confirmatory bias (Thomas Gilovich). In other words when people look for evidence they tend to look for information that confirms their ideas. So now when I visit my mother and she offers me my vitamin c supplement I think of it as her way of saying that she loves me and cares about me.
But I found a great cure for headaches!