It is well documented that people are deficient in vitamin D. The same holds true for dogs.
Is there a clearly defined “optimum” vitamin D blood level for canine health?
The ideal vitamin D level in dogs and cats is not known, but research has identified sufficient levels of vitamin D. There are several laboratories that perform vitamin D testing for animals, including Veterinary Diagnostics Institute (VDI), ANTECH Diagnositcs, and Michigan Diagnostic Center for Population and Animal Health (MDCPAH). At VDI, scientists assess total 25-hydroxy vitamin D (calcifediol), both D3 and D2 from a blood serum sample. Results fall into one of three categories:
- Deficient (less than 30 ng/mL)
- Insufficient (30 – 100 ng/mL)
- Sufficient (100 – 120 ng/mL)
VDI recommends the amount of vitamin D to supplement. Their recommendations are meant to get the pet into the low end of the sufficient range. Blood serum levels are rechecked in 8-12 weeks.
VDI seldom finds animals that have levels of vitamin D that are too high unless they have rodenticide toxicity or were overdosed with synthetic vitamin D. Vitamin D overdoses may occur either by diet misformulation, diet cross-contamination, or over supplementation.
Is there a clearly defined “deficiency” level?
It depends on the laboratory that is doing the testing. Labs may have different definitions of deficiency.
In a 2015 Tufts University study funded by VDI on the effects of diet on serum D levels , researchers looked at serum vitamin D levels in 320 dogs represented by 3 breeds of dogs: Golden Retriever, German Shepherd and White Shepherd.1 Most dogs were fed commercial diets from 40 different manufacturers. Some dogs were fed homemade diets or a combination of commercial and homemade diets. Differences in vitamin D content among manufacturers were statistically significant. A table including each manufacturer and the range of serum vitamin D levels is available in the study.
The study found that dogs that ate homemade diets had the largest range of serum vitamin D levels. They also found that some dogs on home-prepared diets had the most deficient vitamin D levels. According to VDI, raw diets were more likely to show near sufficiency.
Do most commercial pet foods provide adequate vitamin D for dogs?
No. Pet foods are formulated to meet minimum nutrient requirements set forth by AAFCO, and they are not formulated to meet optimal requirements of vitamin D for pets. The Tufts University study did not evaluate vitamin D content in the food, but it evaluated serum levels in the dogs. I spoke to a representative from VDI, and they recently tested 3 Golden Retrievers, all with the same body weight and eating the same diet. Each dog had a different serum vitamin D level.
According to VDI’s research and testing, we can see that every animal is unique. Each animal has its own variances, particularly in their ability to absorb and utilize vitamin D. Vitamin D absorption depends on good digestion. In my opinion, if vitamin D levels are insufficient, it may be as much of a matter of addressing digestion as it is an issue of providing more vitamin D.
In part 2 of the post, we will cover recommendations for vitamin D supplementation. Stay tuned for more information coming soon.