29/10/2020
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Vitamin D for dogs – the art of just enough
CAN DOGS GET ENOUGH VITAMIN D FROM EXPOSURE TO THE SUN?
A lot of animals, such as human, have 7-dehydrocholesterol (7-DHC) in their skin, which can be photochemically converted to vitamin D3 when exposed to the sun. Dogs, however, do not have enough 7-DHC in their skin. They can only get vitamin D from their diet.
VITAMIN D IN DOGS
Vitamin D aids in the absorption of calcium and phosphate, increases bone cell activity, influences the formation and growth of long bones, and speeds the healing of fractures. Dogs lacking vitamin D have higher chance to get heart disease, joint inflammation, skin and coat problems, cancer, vision problems, depression, mental illness, infections, inflammatory bowel disease, dental problems, hyperparathyroidism, and kidney disease.
TOO MUCH OF A GOOD THING IS BAD
Vitamin D is fat-soluble, which can be accumulated in the body. Too much vitamin D can create heart disease, kidney failure and artery problems as well as anorexia. It can be life-threatening in serious cases.
REASONS FOR OVERDOSE OF VITAMIN D IN DOGS
1. accidentally eating cholecalciferol rodenticides – cholecalciferol is the chemical name for vitamin D
2. taking too much vitamin D supplements
3. eating commercial dog food containing too much vitamin D
RECALLS OF DOG FOOD WITH EXCESSIVE VITAMIN D BY MAJOR BRANDS
In 2018-19, some dog food manufacturers recalled dog food products, including some prescription diets, due to excessive amount of vitamin D. According to FDA, some of the dog food contained potentially toxic amounts of vitamin D, as much as 70 times the intended amount in some cases. Similar incidents also happened in 1999, 2010 and 2016 respectively.
WHY DID IT HAPPEN?
It is said to be a vitamin D formulation error in such dog food. In order to meet the AAFCO standard for “complete and balanced diet”, manufacturers add vitamin and mineral premixes to the food. These premixes are synthetic and purchased instead of being formulated by the manufacturers themselves. This could also be the reason for this error to affect multiple food manufacturers during the same period of time. In addition, uneven mixing can also be part of the problem.
MOST DIET LACKS VITAMIN D – A PANDEMIC IN DOGS
Although vitamin D toxicity happened more than it should, it is actually not as common as vitamin D deficiency, because:
1. AAFCO suggests the required vitamin D in dog food to be between 500 – 5000 IU per kg, which the differences are significant. However manufactures do not normally indicate the amount in their food.
2. The vitamin and mineral premixes are synthetic, which don’t always behave the same way food-based vitamins do
3. Food sources of vitamin D include fish, liver, eggs and dairy products. Unfortunately, none of these food sources contain enough D to meet minimum nutrient requirements. Dogs that are fed raw or homemade fresh food diets without the above-mentioned food sources definitely lacks vitamin D.
HOW DO WE ACHIEVE “JUST ENOUGH” VITAMIN D?
- Since every dog’s requirement for vitamin D is different (even same breed that’s fed the same diet), and there is no comprehensive research on vitamin D and adult dogs, there is really no rule of thumb for us to follow
- The only way to know if a dog has enough vitamin D is to test
- Do not feed any vitamin D supplement without any confirmed test result
- Include natural food sources containing vitamin D into your dog’s diet
- If your dog does not eat any of these food sources, you may feed cod liver oil, which contain higher amount of vitamin A and D than other food sources. Consider a dosage by reviewing your dog’s diet holistically.
I hope the above information forms a good foundation for your conversation with your vet in the next visit!
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Further readings:
FDA: Vitamin D Toxicity in Dogs
https://bit.ly/3jFMUEN
More Recalls of Toxic Pet Food, Is Your Brand Implicated?
https://bit.ly/3kBJ6G7
Vitamin D: What Your Dog Wants You to Know
https://bit.ly/3ec6O9C
Photosynthesis of vitamin d in the skin of dogs, cats, and rats
https://bit.ly/3ms7xGs
Current knowledge of vitamin D in dogs
https://bit.ly/34B65vh
An Evaluation of the Vitamin D3 Content in Fish
https://bit.ly/2G6FQUd