Dietary Erythorbic Acid Does Not Affect Urine Oxalate Concentration in Healthy Adult Cats
Hill's Pet Nutrition, Inc.
Topeka, KS, USA
Erythorbic acid (isoascorbic acid or D-araboascorbic acid) is a stereoisomer of ascorbic acid (vitamin C) and is used as a processing aid in some pet foods. Similar to vitamin C, erythorbic acid can be absorbed, metabolized, and excreted in the urine of animals when ingested. Therefore, erythorbic acid could potentially be metabolized in the body to oxalate that is excreted in the urine. Increased urinary oxalate concentration is known to increase the risk of urinary calcium oxalate stones in cats and other animals. The objective of this study was to investigate whether dietary erythorbic acid affects urine oxalate concentration in cats.
Twenty-four healthy adult cats were used in an unbalanced crossover study. A nutritionally complete and balanced dry cat food was used as a control food, which contained an undetectable amount of erythorbic acid (< 0.5 ppm). Three test foods were made by adding various amounts of erythorbic acid to the control food at the expense of starch. The test foods contained 90, 203, or 348 ppm erythorbic acid. All cats were fed the control food for 2 weeks (washout period) and then fed one of the test foods or the control food for another 4 weeks (test period). Blood samples and 24-hour urine samples were collected at the end of the washout period and the test period. Food intake was measured daily and body weight weekly.
Intake of erythorbic acid did not affect urine oxalate concentration (r = 0.26, p = 0.083) nor urine oxalate excretion corrected by urine creatinine (r = 0.18, p = 0.235). Similarly, intake of erythorbic acid had no effect on urine vitamin C concentration (r = 0.11, p = 0.451), urine volume (r = -0.04, p = 0.817), or urine pH (r = 0.24, p = 0.102). Plasma erythorbic acid was undetectable (< 0.5 ppm) in cats fed any of the test foods. Plasma vitamin C concentration was not affected by dietary erythorbic acid. Urine erythorbic acid was undetectable (< 0.5 ppm) in cats fed the test foods containing less than 348 ppm of erythorbic acid. Urine erythorbic acid concentration was 8.24 ± 7.61 ppm in cats fed the food containing 348 ppm erythorbic acid. Food intake and body weight were similar among dietary groups during the study.
This study demonstrates that dietary erythorbic acid up to 348 ppm does not affect urine oxalate concentration, urine pH, and urine volume in healthy adult cats.