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WHAT IS IT
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.
WHAT DOES IT DO
Vitamin D is well-known for its role in calcium and phosphorus regulation. This is critical 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 prominent 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.
However, 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 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 status. Vitamin D has been shown to beneficially impact different autoimmune disorders.
So then, it is quite clear that while vitamin D is critical for healthy bones, it truly is important for overall well-being.
Vitamin D is able to do its job well by working with vitamin A and vitamin K. As mentioned in the previous lesson, 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 one another. Furthermore, I 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.
It is not incredibly common to see situations of acute malnutrition regarding vitamin D in the United States because commercial foods utilizing 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. It would not be outlandish to theorize 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. 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 and 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.
As mentioned, 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.
FOOD SOURCES | Cod Liver Oil, Eggs, Oily Fish, Some Pork, Liver*
As mentioned, 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.
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 lifestyle of the animal.
Notice that sunshine is not on the list. In my opinion, there is no convincing evidence that dogs can reliable amounts of vitamin D from the sun (through synthesis in the skin)- see sources cited.
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).
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.
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 as food contains vitamin D3- but other similar compounds. 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. However, it is still important to supplement when vitamin D needs are not met by food intake.
TOPPING COMMERCIAL FOODS | 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 lesson, cod liver oil can be used (with great results) but it needs to be carefully selected and dosed.
There is some 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 FISH:
Note on feeding sardines or other fish raw: https://therawfeedingcommunity.com/2018/05/19/thiaminase-in-raw-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 DOES A DOG NEED?
The vitamin D requirements for adult dogs is not backed by as much solid research as preferred. The vitamin D requirements for puppies was extrapolated to adults. We really do not have a great idea of how much vitamin D an adult dog needs. 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. Moreover, because AAFCO foods can provide suboptimal vitamin D, carefully selected kibble toppers make a great addition but are not necessarily always required.
Discovering how much vitamin D is needed as a starting point can be done by getting your dog’s metabolic weight. Your dog’s metabolic weight is their weight in kilograms raised to the power of 0.75. (kg^0.75). Then you multiply the metabolic weight by the recommended allowance on this chart (the NRC requirements). However, you can skip all of that and simply use the calculator that I built here.
- Identify vitamin D in the current diet
- Where is the vitamin D in the diet? How often is vitamin D fed?
- Is this a good source?
- Is it plant based? Animal based?
- How much is in the diet?
- Applicable for homemade diets and some commercial whole food diets that provide ingredient amounts,
When providing ingredient amounts, please include your dog’s age, weight, and ideal weight.
https://www.westonaprice.org/health-topics/abcs-of-nutrition/from-seafood-to-sunshine-a-new-understanding-of-vitamin-d-safety/ (careful, not all applicable to dogs)
If you have Canine and Feline Nutrition- Vitamin D section from the Vitamins Chapter
Human Related Reference Guide: https://lpi.oregonstate.edu/mic/vitamins/vitamin-D
NRC Nutrient Requirements of Dogs and Cats (2006)
Canine and Feline Nutrition