Vitamin D metabolism in dogs and cats and its relation to diseases not associated with bone metabolism
Zafalon, R.V.A. et al.
2020
Journal of Animal Physiology and Animal Nutrition

Unlike other animals, dogs and cats are not able to synthetize vitamin D in the skin through sun exposure; they are dependent on the dietary intake. Both forms of vitamin D include cholecalciferol D3, found in animals products and ergocalciferol D2 found in plants.
This review compiles in a table the serum/plasma 25(OH)D concentrations observed in dogs and cats with different diseases, as well as those observed in healthy animals.
Low levels of serum 25(OH)D were detected in several cases of gastrointestinal diseases in dogs and cats; the same trend was observed in dogs with cancer. Additional studies show evidence of involvement of Vitamin D and heart disease and modulation of the immune system.
However, it is not clear whether lower vitamin D concentrations are the cause or a consequence of these diseases- Additional studies are necessary to determine the dietary requirements of vitamin D in pets and to assess the potential beneficial effects of vitamin D supplementation on the onset and prevention of diseases.