Vitamins & Minerals 101 | Vitamin A
with Savannah Welna of FeedThyDog, Nutrition Advocate

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Vitamin A


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EDIT NOTE FOR AUDIO: Itchy dog AND disturbance to stools/digestion is common in immunologic adverse food reactions


WHAT IS IT


Vitamin A is a fat soluble vitamin that is essential for life. Vitamin A itself does not occur in plants, but its precursors (carotenoids) do. In animal products, such as liver, vitamin A is highly bioavailable.


WHAT DOES IT DO


Vitamin A helps the dog’s eyes, skin, and immune system- especially the gut! Deficiencies can range from eye disturbances, immune dysfunction, and even death. Because vitamin A is so important for cell proliferation and differentiation, vitamin A plays a major role in development. Vitamin keeps the eyes moist and functioning and skin smooth.


There is something called the gut associated lymphoid tissue. Here the immune system does “training.” The gut is constantly exposed to the environment and a healthy gut is careful about what can enter the body. When particles make their to the intestinal barrier, the immune system must respond appropriately.  Vitamin A is needed to make retinoic acid- which is essential for this response. This is where the immune system “trains” to identify which things require an immune response.


Click here for image.


So common in the dog world are adverse food reactions. Vitamin A is essential for the immune system to properly train and recognize things that are harmful and which things that are not (such as food antigens!). Growing dogs (and adults, too) should be provided with adequate vitamin A from high quality sources.


While dogs can get vitamin A from plant foods- like sweet potato- the body has to work a bit harder to convert provitamin A to active vitamin A. Any disturbance in this process can result in sub-optimal vitamin A status. However, beta-carotene (provitamin A) from plants is still beneficial! Independent from its function as a precursor, it has been shown to function as antimutagens and anticarcinogens. It protects against free radicals. So don’t skip the liver or the orange and green veggies!



EXCESSES


Too much vitamin A is relatively rare in North America and toxicosis can include joint pain and requires a carefully managed diet. That being said- vitamin A and vitamin D work synergistically. It should be noted that excess vitamin A can hurt vitamin D status and excess vitamin D can hurt vitamin A. It is best to provide theses in balanced amount- making sure both are at optimal levels in the diet. Very often, vitamin D is missing from homemade diets unless oily fish and eggs are fed regularly.


Something else that is good to know- zinc is required for the metabolism of vitamin A. Zinc can often be low in homemade diets as well. It is essential that adequate zinc, D, and A be provided in the diet.



FOOD SOURCES | Liver, Cod Liver Oil, Sweet Potato, Pumpkin, Leafy Greens


Liver is the richest source of vitamin A! Chicken, beef,, duck, turkey..etc. all contain varying amounts of vitamin A. As mentioned above, orange plants and leafy greens provide provitamin A- but the dog has to work harder to make active vitamin A. 


There are some instances where a dog cannot have liver. In those instances, cod liver oil (NOT fortified) can provide an excellent source of both vitamin A and Vitamin D. I prefer Green Pastures Fermented Cod Liver Oil (with butterfats) because it provides non-excessive amounts of high quality vitamin A and D, 


In a homemade diet, these two options will provide all the vitamin A the dog needs.


TOPPING COMMERCIAL FOODS | Pumpkin, Sweet Potato, Leafy Greens, & CAREFULLY dosed liver or cod liver oil 


Properly formulated commercial foods should have enough vitamin A and so adding more can be dangerous. However, because there are beneficial compounds in liver (and cod liver oil), some can be added to kibble in very small amounts. Vitamin A from plant foods is absolutely beneficial- especially if you are feeding kibble because kibbles are a poor source of antioxidants. Leafy greens, cooked pumpkin, and cooked sweet potato (higher calories) are great sources of vitamin A. 


HOW MUCH DOES A DOG NEED?


Discovering how much vitamin A 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. 


MAIN POINTS


  1. Cod liver oil, liver provide bioavailable vitamin A that are toxic in high amounts. In proper amounts, these are excellent sources of vitamin A.
  2. Plants contain provitamin A which dogs can convert to an active form- but toxicity is not of a concern. This would not be appropriate for puppies as the sole source of vitamin A.
  3. Beta-carotene serves beneficial functions outside of vitamin A and is a great addition to nearly all diets- generally speaking.
  4. Vitamin A is critical for life
  5. Vitamin A status can be affected by sub-optimal zinc, excess vitamin D, low levels of zinc, underfed dogs in general, sub-optimal fat intake. and poorly digested commercial foods or underfed commercial foods.


RECOMMENDED READING


  1. https://www.dsm.com/markets/anh/en_US/Compendium/companion_animals/vitamin_A.html
  2. If wanting to learn more about adverse food reactions.


SOURCES


  1. NRC Nutrient Requirements of Dogs and Cats 2006
  2. DSM (link above)
  3. Canine and Feline Nutrition (Awesome textbook)
  4. Chris Masterjohn, PhD- varying podcasts


ACTIVITY


  1. Identify the form and vitamin A in the current diet
  2. Participants share foods and we identify where vitamin A is in the diet
  3. Is this a good source? 
  4. Is it plant based? Animal based? 
  5. Any provitamin A present in both the commercial or homemade diet?
  6. If adding fish oil- did you accidentally select cod liver oil when vitamin A and D was not needed?
  7. How much is in the diet?
  8. Applicable for homemade diets and some commercial whole food diets that provide ingredient amounts,