Agree about taking vitamin C and Zinc - when I was teaching, I kept on getting colds/occasional flu,so I started taking a soluble supplement every morning and Vitamin D most of the year (out of desperation
) and it seemed to work. It is now part of my routine.
However, I have no symptoms of an illness at present (thankfully) but have had tests for cholesterol level (high, so started eating more nuts and oats, trying to lay off "fatty" foods but I think my cholesterol level is influenced by my genetic make up) and for prostate cancer (sensible thing to do in my opinion, thankfully all clear).
If I were to wait for symptoms, odds would be very much stacked against me.
Over the years, with no symptoms, I have had Tetanus, BCG etc and most recently Covid vaccinations.
Both daughters have had HPV vaccination. Wife and daughters have smear tests and checks for breast cancer - all with no symptoms.
Also fell off my pushbike a few years ago and had a had x-ray (chipped lunate bone) which showed early signs of arthritis, so something was found which was not related to my "condition".
Eminently sensible to have diagnostic testing and preventative medicine/courses of action in my opinion.