Vitamin D: The Critical Role it Plays in Your Pet's Health

You’ve heard of vitamin D. It’s commonly referred to as “the sunshine vitamin.” 

While humans have the ability to get what they need from the sun, cats and dogs aren't so lucky. We'll get to that in a minute. 

Our pets have to get vitamin D from their diet. A vitamin D deficiency can cause poor muscle and immune function, inflammation, and heart and kidney disease. Low levels of vitamin D may also increase the risk of certain cancers.

But wait … while you don’t want your pet to have a vitamin D deficiency, you also don’t want him to have a vitamin D overload.  

So what is the right amount of vitamin D for your pet? Well, that depends. But not to worry. We’ll walk you through the basics to answer questions like:

• What is vitamin D?
• Where does vitamin D come from?
• What does vitamin D do?
• Can vitamin D be toxic?
• What are the symptoms of vitamin D toxicity?
• Does vitamin D cause (or prevent) cancer?
• Is there a link between vitamin D and other diseases?

What is vitamin D?

Vitamin D is a fat-soluble hormone (that means it’s stored in fat). It regulates calcium and phosphorus levels, which are crucial for healthy bones and muscles. Vitamin D is also known to reduce inflammation, boost immune function and promote cell growth. 

Where does vitamin D come from?

Humans have 7-dehydrocholesterol (7-DHC) in their skin. When ultraviolet (UV) rays from the sun penetrate the skin, a photochemical reaction takes place causing the 7-DHC to be converted into vitamin D. 

Cats and dogs have very little 7-DHC in their skin, so they can’t effectively use sunlight to generate vitamin D. 

FACT:
7-DHC is also the precursor to cholesterol, so rather than using it to transform UV rays into vitamin D, pets may be converting 7-DHC into cholesterol instead.

Cats and dogs rely on food to deliver vitamin D. 

Most commercial pet foods contain the minimum recommended amounts of daily vitamin D. If you’re feeding a homemade diet, or if you just want to give your pet a boost, add a supplement to make sure you’re satisfying his nutritional requirements.

What does vitamin D do?

Vitamin D enters your pet’s body through his diet and is absorbed in his small intestine. It moves through the bloodstream to the liver where it changes into a form that can be stored in fat for later use. 

What needs to be used immediately moves to the kidneys where it changes into a form that can bind to the vitamin D receptors (VDRs).

Vitamin D receptors are located all over the body. When vitamin D binds to VDRs, it can turn genes on or off, including genes that activate immune function and inflammation. 

Binding also triggers the parathyroid glands (four small glands in the neck) to release some of the calcium stored in bones. 

It then helps that calcium to be absorbed in the small intestine and kidneys. Calcium is important for muscles to move and for nerves to send messages between the brain and the body.

Vitamin D also helps the small intestine and kidneys absorb phosphorus. Phosphorus is important for the growth, maintenance, and repair of cells and tissues. Both calcium and phosphorus are important for the formation of strong bones and teeth.

Can vitamin D be toxic?

Yes.

Since vitamin D is fat-soluble (it can’t be eliminated via urine), it is possible for your pet to experience vitamin D toxicity if they get too much. 

How much is too much?

It can take as little as 0.1 mg of vitamin D per kg of body weight to cause vitamin D poisoning in cats and dogs. A 2 mg dose of vitamin D per kg of body weight could be fatal.

Toxicity may cause serious problems such as hypercalcemia (too much calcium in the blood). That happens when too much vitamin D stimulates the release of too much calcium. 

Vitamin D toxicity may also cause osteochondrosis (inflamed joints). This happens when too much vitamin D negatively affects the genes responsible for immune response and inflammation.

What are the symptoms of vitamin D toxicity?

Visible symptoms of Vitamin D toxicity may include:

• Vomiting
• Loss of appetite
• Frequent urination
• Increased thirst
• Excessive drooling
• Weight loss

These symptoms can be indicative of other serious health conditions, too. If you suspect your pet has vitamin D toxicity, take him to the vet right away.

Does vitamin D cause (or prevent) cancer?

We’ve been told over the years that too much sun exposure can cause cancer. Which begs the question, does vitamin D cause cancer? Is there any correlation between vitamin D and cancer?

There has been a lot of research in recent years on the relationship between vitamin D and cancer in pets. Contrary to popular belief, research has shown that cats and dogs with sufficient levels of vitamin D tend to have fewer cases of many types of cancer, particularly breast, colon and rectal cancers.

One study looked at two groups of dogs, those with tumours and those without. The dogs with tumours had low levels of vitamin D, while the healthy dogs had a sufficient amount of vitamin D. 

In a different study, two separate groups of dogs with spleen cancer had low levels of vitamin D, while the healthy group of dogs had a sufficient amount of vitamin D.

In many other studies comparing levels of vitamin D in animals with various cancers, the results seem to support the hypothesis that lower levels of vitamin D correspond with a higher risk of cancer.

Is there a link between vitamin D and other diseases?

There may be a link between low levels of vitamin D and diseases in the intestines, heart and kidneys. 

There may also be a link between low levels of vitamin D and feline immunodeficiency virus (FIV). 

But researchers aren’t sure if vitamin D increases the risk of these diseases or if the diseases led to low levels of vitamin D by reducing how much the body is able to absorb.

It’s the chicken and the egg.

What we do know is that vitamin D plays a crucial role in your pet’s health. If you’re unsure whether your pet is getting the right amount of vitamin D, talk to your vet. They’ll help you figure out if your pet would benefit from a supplement.