h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Whilst the vitamin C connection with cold avoidance is not proven, I have a friend who tends to eat a kiwi fruit (one of the most vitamin C-rich fruits, I'm told) every day to ward off colds. Occasionally she runs out, either forgetting to buy more, or because the shops have run out. On three such occasions she has caught a cold within a week.

I tend to go with drinking unbelievable quantities of orange juice. That and reacting to the first signs that I might be about to go down with a cold - I always make sure I'm drinking plenty (non-alcoholic drinks - water and OJ mostly), and that I try to get as much sleep as I can, preferably waking up when my body wants to, not when an alarm goes off. (That last bit might be impractical, depending on your work arrangements, but putting it into practice when I can has meant I'm the only person in a house of 3 not to catch a cold in the past. I fly a lot, and regularly teach groups of 20+ people for a week at a time, so I'm always being exposed to lots of people I've never met before, usually an ideal way to catch an illness. And the last time I did get a cold was when I was unable to get as much sleep as I required due to work.)