Many people inquire about the possibility of over consumption of supplements. The water soluble vitamins such as Vitamin C and the B vitamins are not cumulative and are not stored in the body. Vitamin C is flushed out through the urine as oxalates and can be detrimental in the respect that high levels of oxalates can lead to calcium oxalate uroliths in the urinary tract.
Companion animals do not have a requirement for dietary ascorbic acid. Dogs and cats can produce endogenous ascorbic acid in the liver from either glucose or galactose. Therefore, vitamin C supplementation is rarely needed and unnecessary. More attention needs to be given for supplementing with fat-soluble vitamins.
posted by Rob Mueller