Vitamin D is a fat soluble prohormone. There are two major forms of vitamin D, D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). It is responsible for promoting the mineralisation of bones. It also aids the absorption of calcium & phosphorous by increasing absorption from the digestive tract & reducing urinary calcium loss &  regulates blood calcium levels. It is produced in the fur (or skin in humans)  upon exposure to sunlight and also ingested in small quantities via food. Foods containing vitamin D include fish, liver, dairy products & egg yolk.

Vitamin D toxicosis (also known as hypervitaminosis D) is caused by the accumulation of toxic levels of vitamin D. The most common causes are cholecalciferol rodenticide poisoning, treatment of hypoparathyroidism (supplementing with vitamin D3), over-supplementation with vitamin D3 in the diet, & ingestion of plants containing calcitriol glycosides.

What are the symptoms of vitamin D toxicosis?

Vitamin D toxicosis causes hypercalcemia (abnormally high blood calcium levels), which results  in the calcification of various tissues & the intestinal tract, skeletal abnormalities & eventually renal failure, cardiac upset & GI upset.

• Vomiting
• Diarrhea
• Anorexia
• Increased thirst
• Increased urination
• Depression
• Pain in bones
• Gastrointestinal or pulmonary hemorrhage (bleeding from the lungs)

How is it diagnosed?

Your veterinarian will perform a complete physical examination & obtain a medial history from you including questions on possible exposure to rodenticide or vitamin supplementation in the diet.

He may wish to perform the following tests;

Biochemical profile which may reveal hypercalcemia (high blood calcium levels), hyperphosphatemia (high blood phosphate levels), and azotemia (high urea levels in the blood).

X-Ray may reveal mineralisation of certain organs.

How is it treated?

• Induce vomiting for acute exposure to a rodenticide.
• Activated charcoal to prevent further absorption.
• Stop supplementation immediately.
• IV fluids to treat & correct dehydration if necessary.
• Reduce serum calcium. This may be accomplished by diuresis (facilitation of increased urine output) with normal saline solution, furosemide or prednisolone.
  

Vitamin A is a fat soluble vitamin which accumulates if overdosed. It has multiple functions within the body including Vitamin A helps in the formation and maintenance of healthy teeth, skeletal and soft tissue, mucous membranes, and skin.  Vitamin A is stored in the liver, and is released in small amounts as it is needed.

Plants don't actually contain vitamin A but carotin. Vegetables such as carrots are high in carotenoids & most animals, including  humans are able to convert carotene from plants into active vitamin A. Cats however are unable to do this as they lack the necessary enzyme, and therefore need to obtain vitamin A from animal tissue, especially liver.

Cats fed a diet containing too much  vitamin A can be harmful to cats & result in hypervitaminosis A.

What are the symptoms of vitamin A toxicosis?

Chronic cases can show ankylosis fusion of cervical vertebrae & elbow joints, making grooming painful & therefore cats may have an unkempt appearance.

Which foods are high in Vitamin A?

Liver, cod liver oil & vitamin supplements are all common causes of hypervitaminosis A in cats. According to Neils Pederson in his book Feline Husbandry - Diseases & 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.

How is it diagnosed?

A diagnosis will be made by obtaining a dietry history & clinical signs. Your veterinarian may wish to take x-rays to check the condition of the cervical spine & forelimbs.

How is it treated?

Switching your cat to a nutritionally satisfactory diet. Bony changes are generally irreversible, however other symptoms should resolve once a proper diet is fed.

Placing food & water bowls on a platform may ease pain for your cat.

Your veterinarian may prescribe anti-inflammatories or analgesics.

References:

[1] The Feline Patient - Gary D. Norsworthy, Mitchell A. Crystal, Sharon K. Fooshee & Larry P. Tilley.