Vitamin D regulates calcium and phosphorus absorption and is essential for building and maintaining strong bones and teeth. Here is another unique aspect of cat biology: unlike dogs and humans, cats cannot efficiently synthesize vitamin D through their skin when exposed to sunlight. Their fur blocks UV radiation, and the enzyme pathways in their skin are insufficient for meaningful production. This means your cat depends entirely on dietary vitamin D, primarily from animal-based sources like fish, egg yolks, and liver. Vitamin D also supports immune function and proper muscle contraction. Because it is fat-soluble, vitamin D is stored in the liver and fatty tissue, making both deficiency and toxicity possible depending on dietary intake.
A small piece of cooked salmon (about 30g) provides roughly 100–150 IU of vitamin D — your adult cat needs approximately 28–100 IU per day, easily covered by regular fish-containing meals or quality commercial cat food. Unlike dogs and humans, your cat cannot make vitamin D from sunshine, so dietary sources are the only option.
0.0% of daily nutrient intake
Vitamin D makes up 0.0% of your cat's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Weakened bones (osteomalacia), rickets in kittens (bowed legs, enlarged joints, stunted growth), muscle weakness, and increased susceptibility to fractures. Deficiency develops slowly because the body stores vitamin D.
Vitamin D toxicity is dangerous and more common in cats than deficiency, usually from accidental ingestion of rodenticide (cholecalciferol-based) or over-supplementation. Symptoms include excessive thirst, frequent urination, vomiting, loss of appetite, kidney damage from calcium deposits, and potentially death. Never supplement vitamin D without veterinary guidance.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 28 | 100 | IU | Cats cannot synthesize vitamin D from sunlight and depend entirely on dietary sources. Fish is the richest natural source. |
| Juvenile | — | 50 | 125 | IU | Growing kittens need adequate vitamin D for calcium absorption and proper bone development. |
Source: NRC 2006, AAFCO 2024
Vitamin D is essential for calcium absorption in the intestines and directs calcium into bones where it is needed. Without adequate vitamin D, dietary calcium passes through unabsorbed.
What this means: If your cat shows signs of calcium deficiency despite adequate calcium in the diet, check vitamin D status. Since cats cannot make vitamin D from sunlight, dietary sources (fish, eggs) are the only option. Ensure the diet includes both minerals together.
Vitamin D regulates phosphorus absorption alongside calcium. Adequate vitamin D ensures phosphorus is properly absorbed and directed into bones and teeth rather than accumulating in soft tissues.
What this means: In cats with kidney disease, both phosphorus and vitamin D metabolism are disrupted. Veterinary kidney diets manage both nutrients carefully. For healthy cats, a balanced diet with fish provides both in appropriate amounts.
