For a dog, vitamin D is an essential nutrient for life, just as it is for all of us.

Most dog parents have questions about vitamin D and their dogs' needs to thrive:

• How much vitamin D is needed to avoid vitamin D deficiency in healthy dogs?
• How much is too much vitamin D?
• And what foods help ensure you provide dietary vitamin D to your dog?

Let's jump in to answer these questions and talk about your dog and sufficient vitamin D to live healthy and well...

What is vitamin D

Vitamin D is a fat soluble vitamin that is essential for life. Vitamin D3 occurs in animal based products while Vitamin D2 can be found in plant based products and is not of significance here.

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What vitamin D does for our dogs

Vitamin D is well known for its role in calcium and phosphorus regulation. For dogs, vitamin D is critical to ensure that calcium and phosphorus a) end up where they should be - hard tissues like teeth, bones; and b) support the mineralization of bone. Acute vitamin D deficiencies would be most serious in growing animals and severe growth issues would develop. Severe deficiencies would result in death.

Vitamin D is also responsible for facilitating calcium and phosphorus absorption in the gut. Adequate dietary calcium reduces the requirement of vitamin D. Likewise, low dietary calcium can negatively affect vitamin D status as vitamin D is being used to increase calcium absorption in the gut.

How valuable is vitamin D beyond bones & teeth

With all we know about vitamin D and important calcium/phosphorous absorption, vitamin D is still being explored for humans and dogs. It is known now that vitamin D’s functions extend beyond skeletal health. Vitamin D plays a role in cellular development and differentiation/function and skin cancer prevention.

Data also indicates that vitamin D plays a role in supporting healing from atopic dermatitis. Vitamin D also functions to support the immune system and reproduction. It has also been shown to beneficially impact different autoimmune disorders.

It's quite clear that while vitamin D is critical for healthy bones, it truly is important for your dog's overall well-being. 

How vitamin D works with A & K to multiply benefits to your dog

Vitamin D is able to do its job well by working with vitamin A and vitamin K. As mentioned in the previous guide, vitamin A in excess hurts vitamin D. The inverse is also true. Therefore, we want enough vitamin D but not too much and we want enough vitamin A and not too much. An excess or deficiency of A, D, and K can hurt the status of the others.

In addition, it can be viewed that these fat solubles are protective of excess of another one. For example, it has been shown that high amounts of vitamin D are toxic without vitamin A because vitamin D requires vitamin A to function. High amounts of vitamin D will require a proportional amount of vitamin A. At normal levels, vitamin D still requires vitamin A to properly bind to cells and fulfill its role. 

You can see why insufficient vitamin levels and the right balance between vitamins matter in our dogs' nutrition.

Vitamin D deficiency

It is not incredibly common to see situations of acute malnutrition regarding vitamin D in the US because commercial foods using nutrient guidelines will provide vitamin A, D, calcium, phosphorus, etc. at levels that prevent acute malnutrition - but not necessarily at levels that support optimal health. So it is worth considering potential issues of suboptimal vitamin D intake. 

Take for example the average homemade raw diet. The average raw diet contains about 5% liver which is rich in vitamin A. The raw diet may or may not contain eggs (which alone will not provide adequate vitamin D) and fish. Both eggs and fish contribute vitamin D - but only some fish contain appreciable levels. More on food sources later.

If we have a homemade diet that is rich in vitamin A and quite possibly is low in vitamin D (exceptionally common), an imbalance of vitamin A and D frequently occurs. While this may not cause acute malnutrition, it likely is not providing optimal health. We might see disturbances to the skin, worsening of some autoimmune disorders, poor gut health, and poor bone health.

What happens with an excess of vitamin D

As we already noted, excess vitamin D hurts the other fat soluble vitamins. It also begins having the opposite effect adequate vitamin D would have. It can cause the calcification of soft tissues and cause bones to become weak - when properly provided it helps keep bones strong and prevents soft tissue calcification. Vitamin D supplements should never be blindly added to commercial foods or blindly given to puppies.

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Where to find vitamin D in food:

Eggs, cod liver oil, oily fish, some pork, liver...

Vitamin D3 is found in animal products and D2 in some plant based ingredients (like some mushrooms). D2 is not effectively used by dogs and the primary intake of vitamin D should come from vitamin D3. 

Eggs, oily fish

Eggs and oily fish provide appreciable amounts of vitamin D. Oily fish alone can provide enough vitamin D while eggs can help round off levels (but it is hard to feed enough eggs alone to provide enough vitamin D).

Eggs are highly bioavailable and most dog owners can reasonably incorporate eggs into their dog's diet to contribute vitamin D (and other nutrients). Oily fish like sardines, mackerel, salmon, etc. are very palatable and provide an appreciable amount of vitamin D and also omega-3 fatty acids which also help support healthy bones.

Cod liver oil

Cod liver oil makes it to the list yet again- and all the precautions apply (watching out for fortified products, not carelessly adding to the diet).. Cod liver oil is a rich source of vitamin A and vitamin D. If using cod liver oil, start small and slowly increase the amount given. It is a very potent form of vitamin D.

Liver, pork

While liver provides some vitamin D, it cannot be relied upon to provide optimal amounts. You would have to feed a lot of liver which would result in high vitamin A levels. Pork can provide appreciable amounts of vitamin D- but the levels depend on the cut of meat and the source.

What about sunshine

Notice that sunshine is not on the list. Vitamin D is often called the sunshine vitamin, although in my opinion based on the research, there is no convincing evidence that dogs can get reliable amounts of vitamin D from the sun (through synthesis in the skin). That said, many dogs seek out the sun's rays and rightfully so - it's great support for their natural circadian rhythms and overall well-being!

The role of vitamin D supplements

Finally, vitamin D can be supplemented if none of the above can be provided in ample amounts. It should be noted that a vitamin D3 supplement is not the same thing as food since food contains vitamin D3 but other similar compounds as well.

Even though we know much about vitamin D3’s role, we do not know about every compound in food and the benefits that may reside in them. However, it is still important to supplement when vitamin D needs are not met by food intake.

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How to add vitamin D to commercial foods with toppers:

Fish, eggs, cod liver oil

Fortunately, vitamin D rich foods do not provide levels that could result in toxicity easily (with the exception of cod liver oil). Eggs and oily fish make a fantastic kibble topper. As mentioned in the vitamin A guide, cod liver oil can be used (with great results) but it needs to be carefully selected and dosed.

There is evidence to suggest that some commercial foods following AAFCO guidelines do not provide enough vitamin D. For this reason, I consider the above foods a beneficial addition for adults as these dogs may be harmed by suboptimal vitamin D intake and may face chronic illness. 

It should also be noted that these foods will provide other beneficial nutrients that are easily destroyed in kibble processing and transportation.

Note on feeding sardines or other fish:

Sardines, mackerel and other smaller oily fish with shorter life spans are best to feed. Salmon is okay - but should be rotated out. Don’t add too much fish because it containers polyunsaturated fat and will increase antioxidant requirements.

How much vitamin D does a dog need

The minimum vitamin D requirements for adult dogs are not backed by as much solid research as we would like. Sticking closer to the recommended allowance for vitamin D is generally a safe bet. Because dogs live lives that vary wildly from their ancestral counterparts, I prefer to make sure vitamin D is provided in the diet through eggs, liver, and fish rather than jump to the conclusion that minimal vitamin D intake is safe - especially in the context of research that supports higher levels in the diet.

Because AAFCO commercial pet foods (meeting guidelines of American feed - not food- officials) can provide sub-optimal/low vitamin D, carefully selected kibble toppers make a great addition, even if not necessarily always required.

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Getting started: figure out your dog's metabolic weight

Discovering how much vitamin D is needed for your dog as a starting point can be done by getting your dog’s metabolic weight.

Try this

Your dog’s metabolic weight is his/her weight in kilograms raised to the power of 0.75. (kg^0.75). Then you multiply the metabolic weight by the recommended allowance of .45 for Cholecalciferol (the NRC requirements).

Steps to evaluate vitamin D in your dog's diet:

1. Identify vitamin D in the current diet
2. Where is the vitamin D in the diet? How often is vitamin D fed?
3. Is this a good source? 
4. Is it plant based? Animal based? 
5. How much is in the diet?

For homemade diets and some commercial whole food diets that provide ingredient amounts, you want to include and consider your dog’s age, weight, and ideal weight as you evaluate ingredient amounts.

When considering vitamin D intake, it’s important to look for a good balance. Vitamin D is beneficial and should be included in your dog's diet, but too much can lead to problems with absorption of other important minerals such as calcium.  Look for dietary sources that provide adequate amounts without going overboard.

(You can also listen as I talk through all this information on vitamin D and your dog in the accompanying audio below.)

Next up in the Basic Nutrition Channel on Dogly

Now that you have a good understanding of vitamin D, continue to the next essential vitamin step-by-step guide on vitamin E.

Or hop over to the Basic Nutrition Channel if you'd like to ask a question in the Community discussion and start any of the other step-by-step guides in Needed Nutrients. If you ever need more personalized nutrition guidance, please reach out!

Sources:

NRC Nutrient Requirements of Dogs and Cats (2006)

Canine and Feline Nutrition

DSM

Current knowledge of vitamin D in dogs

NCBI

Whole Dog Journal

LPI