Improving immune function long-term

Hi James and others,

What ways would you recommend to improve one's immune system and general wellbeing if they are somewhat sickly, prone to colds, bronchial disorders, asthma, and ear infections for example? I am asking for a friend who has these issues so of course there might be other details necessary to know, but in general, it seems as if he is just of a weak constitution and he asked me how he can improve this.

I was wondering if there are things he can take every day over months, for example, herbs like andrographis, or certain foods like coconut oil or ACV, and other things that target lung health in general (he doesn't smoke or drink). He's 26 years old and generally in good shape otherwise.

On the same subject he has an earache that has been around for 4 or 5 days, quite mild, and someone used a little garlic oil dropped into the ear which relieved it temporarily but it keeps creeping back. Any suggestions for this? We did go swimming a lot in a lake last week but I'm pretty sure his ear was hurting before the swimming, although I am sure it did not help.

Thank you, as always!

J