What is Vitamin D and why is it important to dogs?

Vitamin D toxicity in the dog is the main vitamin toxicity which vets and owners will have to deal with.

Vitamin D is a fat-soluble vitamin which is stored in the fatty tissues of the body and liver. Its main function is regulating the calcium and phosphorus balance in the dog’s body. It also promotes the retention of calcium, this makes it important in bone structure and also in nerve and muscle function.

A deficiency in Vitamin D is a rare event these days because most commercial dog foods are well balanced for both minerals and vitamins. But if a dog does not get enough Vitamin D in their diet then they have an increased risk of heart disease and bone disorders such as osteomalacia and rickets can also be a result. There is also a school of thought that low levels of Vitamin D are linked to an increased risk of cancer in the dog.

What is the main importance of Vitamin D to dog owners and vets in practice?

The main importance of Vitamin D is that when swallowed in large enough quantities then serious toxicity can result. This would be the commonest vitamin toxicity which a vet will come across in practice.

This situation normally occurs after accidental ingestion of rat poisons, overdosage of canine vitamin supplements. And the commonest case being when the dog gets accidental access to a large container of the owner’s vitamin supplements. Dogs can often find these appetising.

But how much Vitamin D does it take to cause toxicity in dogs?

Some of the numbers on the web can be misleading. But taking a very careful and safe approach I personally usually start to become concerned only when dose rates exceeding 0.1 mg per kilogram of the dog’s bodyweight are swallowed. { There are 40,000 iu per mg of vitamin D }

In almost all cases the strength of the Vitamin D capsule will be expressed in International units { iu }, you should be able to read this on the label on the container.

So the figure to bear in mind is dose levels of 1,811 or above iu per pound of the dog’s body weight are a cause for concern, below that you are probably in the clear. To be fair most cases of serious vitamin D toxicity that I have dealt with involved much greater amounts than that which I have listed above

What are the symptoms of vitamin D toxicity in the dog? 

Vitamin D is potentially toxic to dogs because it is linked with the metabolism of calcium in the body. Too much vitamin D causes too much calcium (hypercalcemia) in the body, and that is what causes the damage, this could include kidney failure, haemorrhage, and tissue mineralization in the heart, liver and kidneys.

Following an overdose expected symptoms usually start some 12 – 48 hours after ingestion and these could include vomiting, dark diarrhoea containing blood, lethargy, inappetance and drooling in the early stages. Later symptoms could include marked weight loss and seizures. Fatalities are possible where very large amounts have been ingested.

How is Vitamin D overdose treated in the dog and what should you do if you suspect your dog has taken an overdose? 

As with a great many other toxins if you can induce vomiting to recover the swallowed Vitamin D within the first hour after ingestion { Two hours at the very outside } then this may be possible. Please follow this link for precise instruction on how to safely induce vomiting in the dog: LINK

But if you fail to quickly induce vomiting then you should take your dog to an ER vet without delay. They will be able to quickly induce vomiting with prescription drugs. There are drugs which can be used to prevent further absorption of the ingested vitamin D if given early enough. And of course, the vet can give supportive care such as IV fluids should this prove necessary. Some dogs may require a blood transfusion if anaemia is a feature of the disease.

Should your dog have taken a large dose of Vitamin D then be aware that any veterinary treatment can be both expensive and time-consuming. This is because of the high level of supportive care which may be required and the frequent blood test which will be needed?

Prevention of Vitamin D poisoning in the dog.

It is always a good idea to consult with your regular vet before giving your dog any form of vitamin supplementation. Very often if a dog is on a commercial dog food of some kind then such supplements are unnecessary. And if they are given in too high dose toxicity can occur. It is always wise to keep your own vitamin supplements well out of your dog’s reach. And take care with any rodent poisons you may have in your house.