Cats need 13 vitamins to stay healthy: vitamins A, D, E, K, and the full range of B vitamins (B1, B2, B3, B5, B6, B7, B9, and B12). What makes feline nutrition tricky is that cats have several quirks in how they process vitamins that set them apart from dogs and even most other mammals. They can’t make vitamin A from plant pigments, they can’t produce vitamin D from sunlight, and they burn through certain B vitamins faster than other species. Any complete commercial cat food will contain all of these, but understanding why each matters helps you make smarter choices about what goes in the bowl.
Vitamin A: Why Plant Sources Don’t Work
Most animals, including dogs and humans, can convert beta-carotene from plants into usable vitamin A. Cats cannot. Research published in The Journal of Nutrition confirmed that even when cats absorb beta-carotene from food, none of it (or only untraceable amounts) gets converted into vitamin A in their bodies. Cats given beta-carotene instead of preformed vitamin A developed deficiency symptoms just as quickly as cats given no vitamin A at all.
This means cats are strictly dependent on preformed vitamin A, which comes from animal tissues. Liver is the richest natural source, also providing vitamin K, iron, and phosphorus. Kidney is another strong source. However, feeding liver exclusively or in large amounts can actually cause vitamin A toxicity. The safe upper limit for cats is around 100,000 IU per kilogram of diet, roughly ten times the requirement of 10,000 IU/kg. Acute toxicity causes loss of appetite, nausea, skin peeling, tremors, and in severe cases, seizures or paralysis.
Vitamin D: Sunlight Doesn’t Help Cats
Humans and many animals synthesize vitamin D when ultraviolet light hits their skin. Cats essentially can’t do this. In one study, kittens exposed to 15 hours of direct summer sunlight per week saw their vitamin D levels drop at the same rate as kittens kept entirely indoors on the same vitamin D-free diet. Kittens placed under UV lamps fared no better and eventually developed clinical signs of deficiency.
The reason is chemical. Cat skin contains very little of the precursor molecule that UV light converts into vitamin D. The enzyme that breaks down this precursor is too active in cats, leaving almost nothing for sunlight to work with. In the wild, this isn’t a problem because prey animals (mice, birds, small mammals) contain enough vitamin D to meet a cat’s needs. In a domestic setting, the diet has to supply it entirely. Vitamin D toxicity is also a real concern: excessive intake can cause vomiting, excessive thirst and urination within 12 to 48 hours, followed by dangerous calcium buildup that can damage the kidneys, heart, and digestive tract.
The B Vitamins: Higher Demands, Unique Risks
Cats require higher levels of several B vitamins compared to dogs. Niacin (B3) and pyridoxine (B6) stand out in particular. Cats also need reliable dietary sources of thiamine (B1), riboflavin (B2), and cobalamin (B12), among others.
Thiamine (B1) and Raw Fish
Thiamine supports brain and nerve function, and deficiency hits cats hard. The classic cause is raw fish. Fish and shellfish contain enzymes called thiaminases that destroy thiamine on contact, not just in the cat’s body but in any food the fish is mixed with. A cat eating a raw-fish-heavy diet can develop thiamine deficiency surprisingly fast.
The neurological signs are distinctive and alarming. Early on, a cat may seem mentally “off” or lose coordination. A hallmark symptom is severe neck ventroflexion, where the cat’s head drops and stays pointed toward the ground, unable to lift. As deficiency progresses, symptoms can escalate to blindness, rigid limbs, tremors, seizures, and coma. Cooking fish destroys thiaminases, which is why cooked or properly processed fish in commercial diets doesn’t carry the same risk. Raw eggs pose a similar problem: they contain avidin, a protein that destroys biotin (B7), though cooking eliminates it.
Other B Vitamins
Riboflavin (B2) supports energy metabolism and healthy skin. Cobalamin (B12) is critical for red blood cell formation and nervous system health. Cats with chronic digestive diseases sometimes develop B12 deficiency because they can’t absorb it properly from food, which is one of the few situations where a veterinarian might recommend a specific vitamin supplement.
Vitamin E: Linked to Fat Intake
Vitamin E acts as an antioxidant, protecting cells from damage caused by fat oxidation. In cats, the need for vitamin E rises directly with the amount of polyunsaturated fatty acids (PUFAs) in the diet. Fish oil is especially rich in these fats, and over the past 50 years, most reported cases of vitamin E deficiency in cats have been traced to high-PUFA diets without adequate vitamin E.
The minimum requirement is 30 IU of vitamin E per kilogram of dry food, but that number can triple or quadruple for diets high in fish oil. AAFCO recommends that fish-oil-containing cat foods include 10 IU of vitamin E for every gram of fish oil per kilogram of diet. Without enough vitamin E, cats can develop steatitis, sometimes called “yellow fat disease,” a painful inflammatory condition of body fat. It has been experimentally induced in kittens fed high-fish commercial diets lacking sufficient vitamin E.
Vitamin K
Vitamin K is essential for blood clotting. Cats typically get enough from animal-based ingredients in commercial food, with liver being a particularly rich source. Deficiency is uncommon in cats eating balanced diets but can occur with certain poisonings (such as rodenticide ingestion) that interfere with vitamin K’s clotting function.
Why Commercial Cat Food Covers the Basics
Any cat food labeled “complete and balanced” in the U.S. must meet AAFCO Cat Food Nutrient Profiles, which set minimum (and in some cases maximum) levels for every essential vitamin. These profiles exist for two life stages: adult maintenance, and growth and reproduction. The European equivalent, published by FEDIAF, sets similar standards. A food meeting these profiles will provide adequate thiamine, riboflavin, B12, and every other vitamin your cat needs without supplementation.
This is exactly why feeding dog food to cats is a problem. Dogs can convert beta-carotene to vitamin A and synthesize certain nutrients that cats cannot. Dog food formulations reflect those abilities, so a cat eating dog food long-term will develop nutritional gaps, particularly in vitamin A, certain amino acids, and several B vitamins.
When Supplements Make Sense
For a healthy cat eating a complete commercial diet, vitamin supplements are unnecessary and can even be harmful, particularly with fat-soluble vitamins (A, D, E, K) that accumulate in the body rather than being excreted. The situations where supplementation becomes relevant are specific: cats with chronic gastrointestinal disease that impairs absorption, cats on homemade or raw diets that haven’t been professionally formulated, and cats with certain skin conditions where targeted vitamin A therapy may be used.
If you’re preparing homemade cat food, getting the vitamin balance right without professional guidance is genuinely difficult. The interplay between fat content and vitamin E needs, the absolute requirement for preformed vitamin A from animal sources, and the correct ratios of B vitamins all demand careful formulation. A board-certified veterinary nutritionist can design a recipe that accounts for these specifics.