Vitamin A is a fat-soluble vitamin that has multiple functions within the body. It helps in the formation and maintenance of healthy teeth, skeletal and soft tissue, mucous membranes, and skin. Approximately 80% of vitamin A is stored in the liver and is released in small amounts as it is needed. Vitamin A toxicity (also known as hypervitaminosis) occurs when too much vitamin A is ingested leading to toxicity.
The effects of high doses of vitamin A vary depending on the amount given and the age of the cats. Cats can develop either chronic or acute vitamin toxicosis. Acute is sudden onset and occurs when large doses of vitamin A are suddenly ingested, chronic toxicosis occurs more slowly, over a prolonged period of time.
High levels of vitamin A are toxic to the liver, the major storage site of the vitamin.
Excess intake leads to excess bone formation (exostosis), particularly in adult cats. The cervical/thoracic spine and joints are particularly affected. Over a prolonged period of time, complete fusion of the spine can develop.
Kittens can develop loose teeth, gum problems and abnormalities with bone growth. Their bones can easily fracture.
Vitamin A supplemented during pregnancy can result in cleft palate.
How does vitamin A toxicosis occur in cats?
Cats can develop vitamin A toxicosis when they are fed a diet containing foods which are rich in vitamin A, most often this would be a diet high in liver.
Supplementing your cat’s diet with cod liver oil.
Often symptoms are subtle and can take months to develop. One of the first symptoms the pet owner may notice is an unkempt coat. Other presenting signs may include:
Kittens but not adults can develop gingivitis and loose teeth 
Chronic cases can show ankylosis fusion of cervical vertebrae and elbow joints, making grooming painful and therefore cats may have an unkempt appearance. Jaundice may be seen in cats with liver damage.
Which foods are high in Vitamin A?
Liver, cod liver oil, and vitamin supplements are all common causes of hypervitaminosis A in cats. According to Neils Pederson in his book Feline Husbandry – Diseases and Management in the Multiple Cat Household pet mixes obtained from butchers may also on occasion be a cause as they often contain high amounts of liver.
A diagnosis will be made by obtaining a dietary history and clinical signs. Your veterinarian will need to perform some diagnostic tests as well as imaging to assess changes in the bones and joints.
X-rays to check the condition of the cervical spine and forelimbs.
Blood tests to check your cat’s vitamin A levels.
Biochemical profile to check the overall health of your cat, including the liver which can suffer damage from high levels of vitamin A.
Bony changes are irreversible, however, other symptoms should improve once a proper and balanced diet is fed.
The goal of treatment is to relieve discomfort associated with bone changes and may include:
Place food and water bowls on a platform may ease the pain for your cat.
Anti-inflammatories or analgesics to relieve pain.
In some cases, your veterinarian may opt to surgically remove the excess bone growth.
Only feed organ meat to your cats in small quantities and occasionally. Be careful feeding your cat liver, it can be highly addictive to cats who can go on to refuse other types of food.
Never give your cat vitamin supplements unless advised to do so by your veterinarian.
 The Feline Patient – Gary D. Norsworthy, Mitchell A. Crystal, Sharon K. Fooshee and Larry P. Tilley.