The first and most important condition of all: Make sure you are in good shape, well rested and enjoying a diet rich in fruits, nuts and vegetables... and.... make sure you have adequate Vit D levels. It is a cheap supplement and will save you from untold grief.
Try to cut down on red meat during the time that colds are doing the round (fall through winter).
But do not cut down on fat. In fact it is better to use butter than margarine. Much more on that in the Food Science section.
There is something to be said for stews (lots of onions and carrots) during winter.
Extra Vit.C (with rosehips) ; Make sure you have an adequate supply of timed-release Vitamin C on hand. Chewables are good through the day but not for overnight. Too many chewable Vitamine C's are hard on your teeth!
Zinc tablets since our general diet is low in zinc. Braised calfsliver is very high in zinc, as is venison, sesame seeds, pumpkin seeds and low fat yoghurt.
Make a habit of washing your hands often.
At the first Signs
As Dr. Elliot Dick from the University of Wisconsin (Faculty of Preventative Medicine) is in a habit of doing: load up on Vitamin C He takes 2000mgs every hour for three hours, when he feels a cold coming on. Usually it is gone by then but if not he continues with 1000mg per hour.
Not everybody can handle that heavy a dose. Not that it would harm you, but you could get a very loose stool, even diarrhea. Personally we have taken between 4000 and 6000 per day without any side effects and our colds hardly ever lasts longer than three days. i.e. if we get them at all! We have done this now for over 15 years. It wasn't until recently that we discovered the VitD connection and have been taking extra VitD (cheap supplement). As it turns out, it was that little extra we needed.
This winter we have not yet had any colds at all!! (time of writing is end of January 2010)
When you have a Cold
Load up on Vitamin C, at least 4000mg. (4 x 1000mg pills) per day, preferably timed- release. Certainly when you go to bed.
Regular (the chewable type) is through your system in 2 hours flat.
Of course apples and oranges work too.
Make sure you drink lots and take an aspirin every couple of hours.
As a note of interest: Even though Vit E (the natural kind) is not specifically for fighting a cold, in a way it does help since it is the best buddy of Vit C. They work in tandem. Vitamins C and E can regenerate each other and thus potentiate each other's antioxidant effects. In fact, especially for older people, all vitamines are extremely important since the body itself creates more free radicals the older you get and it is the free radical activity that eventually wears out the body.
It has to be aspirin (ASA) not Tylenol (acetaminophen), which is pretty hard on your kidneys and liver
Acetaminophen may increase nasal congestion . That's why cold remedies with Tylenol often are combined with a variety of decongestants.