Vitamin can't manage to perform (5)
I believe the answer is:
enact
'perform' is the definition.
(I've seen this before)
'vitamin can't manage' is the wordplay.
'vitamin' becomes 'E' (E is an example).
'manage' indicates an anagram (I've seen 'managed' mean this).
'cant' is an anagram of 'nact'.
'e'+'nact'='ENACT'
'to' is the link.
(Other definitions for enact that I've seen before include "Put on stage or statute book" , "Decree" , "Put into law" , "Bring in" , "get into law" .)