Contents of mini-vat could supply health supplement (7)
I believe the answer is:
vitamin
'health supplement' is the definition.
(type of health supplement)
'contents of mini-vat' is the wordplay.
'contents of' indicates anagramming the letters (the same contents in another order).
'mini'+'vat'='minivat'
'minivat' with letters rearranged gives 'VITAMIN'.
'could supply' is the link.
(Other definitions for vitamin that I've seen before include "Natural organic substance essential to health" , "Substance aiding metabolism" , "Essential substance in food" , "A, B, C, D, E or K" , "Food constituent" .)