Skeletal and hepatic changes induced by chronic vitamin A supplementation in cats

- Cats that consumed vitamin A in doses equivalent to the safe upper limit did not show abnormal locomotion or clinical signs of liver failure after 18 months of supplementation.
- However, these cats did show subtle skeletal changes and liver pathology, which implies that current National Research Council (2006) safe upper limit for vitamin A for cats might be too high.
- The addition of vitamin D did not influence skeletal pathology in cats during the 18-month study period.
- Compared to cats receiving a control diet supplemented with peanut oil, a fivefold higher intake of vitamin D intake might be protective against the development of liver pathology in cats consuming 100 times as much vitamin A as control cats, but a 65-fold higher dietary vitamin D intake is probably not protective.

The first aim of this study was to determine whether vitamin D supplementation influenced the effects of high vitamin A intake on new bone formation in adult cats. The second aim was to determine whether high vitamin A intake in cats caused liver pathology and, if so, whether the current upper limit for the dietary intake of vitamin A for healthy adult cats would be safe. Twenty-four healthy adult cats were divided into four groups that received a control diet supplemented with peanut oil (control), or peanut oil containing a 100-fold increase in vitamin A (HA), or a 100-fold increase in vitamin A and a fivefold increase in vitamin D (HAMD), or a 100-fold increase in vitamin A and a 65-fold increase in vitamin D (HAHD) over a period of 18 months.Cats did not show abnormal locomotion or clinical signs of liver failure after 18 months of supplementation but did show subtle skeletal changes and liver pathology, suggesting that the current National Research Council (2006) safe upper limit for vitamin A for cats is too high. The addition of vitamin D did not seem to influence bone pathology. While moderately elevated dietary vitamin D levels (HAMD) seemed to protect cats against the liver pathology caused by the consumption of large amounts of vitamin A, higher dietary levels of vitamin D (HAHD) did not seem to be protective.