Good health improves one's mood (6)
I believe the answer is:
cheers
This clue is a double definition.
'good health' is the first definition.
(both can be used as a drinks toast)
'improves one's mood' is the second definition.
(as in cheering someone up)
(Other definitions for cheers that I've seen before include "so long and > much appreciated" , "Hurrahs and oles" , "Ta; gives comfort to" , "Shouts of applause, or drinking toast" , "Shouts of praise" .)