Vitamin D3

Not enough. People can make vitamin D in their skin from sunlight, but cats cannot make enough this way, so they must get it from their diet.

Vitamin D3, or cholecalciferol, is one form of vitamin D, which the Merck Veterinary Manual calls an essential nutrient in the diet of dogs and cats. Merck notes that both species have very limited amounts of 7-dehydrocholesterol in their skin, and that hypervitaminosis D has been linked to excess vitamin D accidentally added to commercial pet foods. Ask your veterinarian about vitamin D for a cat with kidney disease or another medical condition.

Source: merckvetmanual.com

Vitamin D3 is added because cats depend on their diet for vitamin D, which helps the body absorb and use calcium and phosphorus. Fish and liver contain some, but levels vary, so manufacturers add a measured amount to the vitamin premix to hit the target for cats.

Too much vitamin D can raise blood calcium. In a 2018 alert about dry dog foods, FDA listed vomiting and increased thirst among the signs, and said very high levels can cause kidney failure. That alert involved dog foods only. A cat with these signs should see a veterinarian right away.

Source: fda.gov

Vitamin D2, or ergocalciferol, comes from plants and fungi. Vitamin D3, or cholecalciferol, is the animal form. Cat foods usually use D3, and on a label it may read vitamin D3 supplement. Both forms need to be activated by the liver and kidneys before the body can use them.

Pettings gives vitamin D3 4 out of 5 and lists it as a vitamin. It appears on 142 of the 149 dry cat foods we list. Cats rely on dietary vitamin D, and almost every dry food we track adds it. Each food's page shows how it scores overall.