Just wondering

[ETrent]

Please forgive my ignorance - but I am new to the list.  I hear a lot about giving supplements to cats - vitamin C, in particular.  What is the benefit of this for FeVL+ cats?  Since cats, unlike humans, synthesize and produce their own vitamin C - are FeVL+ cats unable to continue to produce it?  What is the added benefit and what is the dosage?  Although vitamin C is a water soluble vitamin - what is the upper limit of this vitamin that is considered toxic?    What are the recommended allowances of the various vitamins for cats and what are the vitamins they require?  Where can I find reputable resource material?   Thank you for your time and your patience.   elizabeth