Does an increase in dietary calcium effect your cat?
As humans we grow up hearing regularly about calcium and how much we need it in our diet, but how important is calcium for a cat? Studies had not been conducted on how dietary calcium levels could affect vitamin D, vitamin D metabolites, and the urinary and fecal mechanisms; and the physiological significance (Passlack et al., 2016). Based upon a previous study on rats they hypothesized that hormonal and excretory mechanisms may be triggered by extremes of calcium levels consumed (Passlack et al., 2016). They expected that there may be interactions that occur between the calcium levels and the vitamin D and phosphorous levels.
Five adult male and five female cats were used as test subjects for this experiment. All members of the group were fed the same diet at the same time, with a rotation of 6 different experimental diets over a course of 6 feeding periods (Passlack et al., 2016). Each of the six diets was fed to the cats in order of the lowest calcium diet to the highest calcium diet; done in order to avoid the higher calcium diets interfering with the data of the lower concentration diets. Each diet lasted for 18 days where 10 days no testing occurred to give the cat’s adequate time to adapt and during the following 8 days the cat’s faeces and urine were collected for testing (Passlack et al., 2016). At the end of each diet one blood test was taken from each cat after 18 hours of fasting and the cats weighted once each week of the study (Passlack et al., 2016). The cats were housed in the same, unchanging, conditions for the first 10 days then separated for the remaining 8 days of each diet. Special litter boxes were used that allowed the urine to separate, with the faeces staying on top the litter, like a typical litter box. The urine and faeces were collected twice each day of the 8 day sample-collecting period. Each of the six diets focused on the increasing calcium and phosphorus levels with each maintaining approximately a 10:9 ratio respectively. The main source of calcium within the diet was dicalcium phosphate.
Based upon the blood work, vitamin D3 and the vitamin D metabolites were not affected by the increasing dietary levels of calcium (Passlack et al., 2016). The change in diets had no effect on: Vitamin D levels, certain Vitamin D metabolites, parathyroid hormone, or the fibroblast growth factor 23. The urea and creatine levels were found to have slightly more variegation, but all were within the normal parameters. The calcium levels in the urine were not elevated, even with the increased calcium diets. However, the increase of dicalcium phosphate increased more than threefold the concentration of phosphorous in the urine (Passlack et al., 2016). The pH of the urine did become more acidic though with the calcium increase. The amount of fecal matter, and concentration of calcium, increased with the calcium increase. The increase of calcium in fecal matter is indicative that the homeostasis of calcium in cats is dominantly regulated by the intestines and not the kidneys (Passlack et al., 2016). In this study the calcitrol levels did not vary between group blood samples, however, the calcitrol precursor metabolites decreased with the increased calcium diets (Passlack et al., 2016). The levels of vitamin D [serum 25(OH)D] were higher, which is opposite to the previous study conducted on rats. Also not correlating to the previous study in rats, there was not a decrease in parathyroid hormone with the increased calcium intake.
The authors and conductors of this experiment take note of the fact that varying levels of dietary calcium have been a subject of study now but that a total deprivation has yet to be studied. Total calcium deprivation could be a good direction of focus to include in a subsequent study, particularly since calcium deprivation was one diet factor observed in the previous study on rats (of which the authors seem to want to compare to on several accounts). Rats and cats are quite similar animals though it is pondering why the authors/ experimenters are seemingly fixated on trying to make direct comparisons to the two studies. This leads me to believe that the experiment was possibly agenda-driven.
Passlack, Nadine et al. February 2016. “Impact of Increasing Dietary Calcium Levels on Excretion and Vitamin D Metabolites in the Blood of Healthy Adult Cats.” PLOS One. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149190. Accessed October 2016.