The kidney is a particularly metabolically active organ, generating high levels of reactive oxygen species which can cause oxidative damage to the kidney. Normally the kidney maintains an environment that suppresses this damage by running antioxidant defense systems which include enzymes such as catalase, superoxide dismutase, nitric oxide synthase, glutathione peroxidase and nonenzymatic antioxidants like glutathione, carotenoids, vitamins E and C, and albumin. When kidney disease is present, the remaining functional tissue becomes hyperactive, which increases metabolic activity and the risk for oxidative stress. At the same time, the reduction in functional tissue results in less available antioxidant activity. This loss of antioxidant potential is worsened by concurrent conditions associated with kidney disease, such as hypertension and anemia (Brown, 2008).
Studies by Scott Brown at University of Georgia have shown that supplemental vitamin E, carotenoids, and lutein in addition to fish oil, slowed degeneration fo kidneys in older dogs.
Although optimal doses are unknown, Brown points out that oversupplementation can be as dangerous as undersupplementation, and settles on a recommendation of 5 IU vitamin per kg of body weight, daily (Brown, 2008).
A study published in 2006 also pointed to benefits in supplementing Vitamins E, C and beta carotene to kidney patients, this time in cats. Yu and Paetau-Robinson, researchers with the Hill's Science and Technology Center, investigated the presence of oxidative stress in cats with chronic kidney disease and whether antioxidant supplements could control the damage. Chemical analyses revealed that, in cats with renal insufficiency, the serum urea nitrogen (BUN) was signifcantly reduced after feeding antioxidant supplemented foods for 4 weeks, but serum creatinine was essentially unchanged. In addition, oxidative damage (as measured by serum 8-OHdG concentration and comet assay) was suppressed by antioxidant supplementation. The doses of antioxidants used per cat can only be approximated, as they were reported in mgs per kg of diet. Using standard calculations, we can guess that the doses each cat received were about: Vitamin E - 46 mg (about 46 -60 IU); Vitamin C - 5 mg; and beta-carotene - 131 ug, which if my calculations are correct, is about 433 IU beta-carotene.
Most authors claim that prescription diets for kidney disease contain enhanced levels of antioxidant, although I was unable to find the levels in company literature. It's probably wise to avoid supplementing antioxidants to animals eating these prescription diets. That's the point - pets with kidney disease often have poor appetites, and it is sometimes difficult to keep them eating any of the prescription diets. These are the pets that might benefit from antioxidant as well as fish oil, supplementation.
Brown SA. Oxidative stress in chronic kidney disease. Vet Clin Small Anim 38 (2008) 157–166
Yu S, Paetau-Robinson I. Dietary supplements of vitamins E and C and beta-carotene reduce oxidative stress in cats with renal insufficiency. Vet Res Comm 30(3):403-413