I made my sketches for "An Apple a Day Keeps the Doctor Away":

 

I also colored in some sketches to see if darkening some areas would make the idea clearer by drawing more attention to the important aspects.

 

 

So far these are the ideas I like:

1. The apple that looks like a lock that has been opened and the symbol of health (red cross) inside it (replacing the keyhole in a regular lock). This conveys the idea that the apple "unlocks" health.

2. The apple with the symbol of pharmaceuticals (a mortar and pestle) inside it. This conveys the idea that the apple contains the medicines that the doctors would prescribe. 

3. The apple inside a puzzle depicting the red cross symbol of health. It says that the apple is the missing puzzle piece that helps you get healthy. 

---------------------------------------------------------------------

 This is a refined sketch for the puzzle concept:

 Here is a refined sketch for the "unlocking health" concept:

 

 

 And here is the refined sketch of the "apple as medicine" concept: