Vitamin A and iron let out (7)
I believe the answer is:
retinol
'vitamin a' is the definition.
(vitamin A refers to retinol)
'iron let out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'iron'+'let'='ironlet'
'ironlet' anagrammed gives 'RETINOL'.
'and' is the link.
(Other definitions for retinol that I've seen before include "vitamin essential for good eyesight" , "certain vitamin" .)