To try and avoid colds (common cold type stuff) I take some various vitamins / supplements. I have no proof that it works. It is subjective.
However, I have been taking a daily mix of OPC type antioxidants (oligomeric proanthocyanadins) since late 2000. (Grape skin extract aka “red wine” extract made from the skins and flesh of purple grapes, grape seed extract, and pine bark extract aka “pycnogenol”). Since around 2003 or 2004 I have added another mix made up of extracts from various purple and red type vegetables and fruits. (Actual names of the two are “OPC-3” and “Maximum ORAC” in case anyone is interested.) I also take 1000-2500mg Vitamin C most days but was taking that before I started the stuff listed above. (I take other supplements and a multi vitamin but that does not factor in to this – they have been added to the above over the last 12 years, except the Vit C and multivitamin and a fish oil which I was already doing – the biggest change happened with the addition of the antioxidants in 2000)
Before 2000, I would regularly get 3-4+ colds a year and they would be pretty strong and last many days. This was a regular occurrence. Since 2000, after I started taking the above OPC antioxidant mix daily (in a liquid isotonic form), my incidence of colds has gone down to 0-2 a year, and they are usually over in 2-3 days, with the worst, drippy nose/can’t think straight part being mere hours instead of 2+ days. I have no objective proof that it is the above antioxidant mix I take, but the change happened right after I started taking it. My wife also started taking it and saw a similar improvement in her life WRT colds.
My kids were started on a kid-size portion of the above, plus a liquid isotonic kids multi-vitamin when they were 1 and they have also had a lot fewer colds than the kids in the neighborhood and than I ever had. They still get an occasional cold, but it is less severe than I would consider normal and less often.
Again, subjective and I have no proof they are related. However, I continue and will continue to take this.
Now, when I do feel a cold coming on, I jam some extra Vit C, and extra garlic tablet or two, and some extra antioxidants for as long as I feel the cold symptoms. I don’t know if it helps to increase the amounts when the cold actually comes on, but I do it anyway. Can’t hurt. This is all stuff you piss out if you overload anyway.
As was mentioned by Panzerr, I’ve heard similar that moderate exercise can help.
And of course, the obligatory stay hydrated and get as much sleep as you can.