Vitamin A is an essential vitamin for cats, dogs, and humans. Deficiency in vitamin A can lead to serious conditions, especially blindness. However, too much vitamin A or hypervitaminosis A can lead to serious toxicity. While somewhat uncommon in North America, vitamin A toxicity is sometimes diagnosed in dogs that are fed primarily table scraps.

What causes vitamin A toxicity?

Vitamin A toxicity is usually caused by eating too much organ meat, especially liver, which contains high levels of vitamin A, or by consuming supplements containing high levels of cod liver oil. There seems to be considerable variability in how susceptible individual dogs are to this problem. Some dogs can eat large quantities of vitamin A and never develop problems while other dogs seem much more prone to develop the problem. This condition is extremely unlikely to develop if you feed your dog a high-quality commercial dog diet produced by a reputable manufacturer.

What are the clinical signs of vitamin A toxicity?

It takes a long time for the clinical signs associated with vitamin A toxicity to develop; symptoms do not usually appear until the dog is at least middle-aged. The most common problem is a form of arthritis in which new bone develops around joints. This leads to stiffness and immobility of the joints; in some cases, the joint may become totally fused. A common site of new bone formation is between the vertebrae of the neck, which interferes with movement of the neck and results in pain and discomfort.

In extreme cases, the dog is unable to move its neck and has difficulty eating. The elbow, wrist, shoulders, and hip joints are also often involved. This can lead to lameness and pain. Owners may notice that the dog cries out when picked up. Many dogs begin to withdraw from contact and spend much of their time hiding. Other clinical signs can include GI disturbances, paralysis, long bone fractures, coagulopathies, and increased liver enzymes/decreased liver function.

How is vitamin A toxicity diagnosed?

Diagnosis is based on a history of being fed foods high in vitamin A, clinical signs, and radiographic evidence from X-rays of new bone formation. Acute ingestion of toxic doses (ingesting a bottle of vitamins for example) can be treated with activated charcoal. Your veterinarian may recommend blood and urine tests to rule out other causes of these clinical signs.

"The damage to the joints and the new bone formation are irreversible..."