Some authors consider that older animals should be provided with increased quantities of vitamins in the ration to overcome reduced ability to digest and/or absorb them from the ration though there is little evidence to support this viewpoint.

Water soluble vitamins are lost from the body in the urine and polyuria such as accompanies chronic renal failure or diabetes are indications for increasing dietary intake to compensate for urinary losses.

Vitamin intake should probably also be encouraged in the presence of reduced liver function.