Also, thanks to Mark Cohen for pointing out potential risks of unbalanced immune-stimulating.
I have a sister now dealing with a mysterious set of serious ailments which has been called Lupus with possible non-Hodgkins lymphoma.
I wouldn't be surprised if injudicious use of trendy immune-stimulators has been a part of her health regimen.
I hasten to say that the problem I see is not with the products, but whether they are used wisely. I would call it unwise to use them as first-line health regimen, in place of the common-sense (and non-dangerous) methods that have already been mentioned.

In those I include: healthy simple foods(preferably organic), moderate (not compulsive) exercise, adequate rest, effective stress-reduction regimen, trying for true self-awareness (includes moderation in use of mind-altering subs, & making your peace with God and people - and music does almost all these things for me!