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All major brands of dog food provide insufficient vitamin D

In a major study from Tufts University , 40 different brands of dog food were evaluated for the amount of vitamin D absorbed and converted to 25-hydroxyvitamin D (25vitD), the primary store and precursor to the active hormone, calicitriol.

In a group of 320 dogs, 25vitD concentrations ranged from 9.5 to 249.2 ng/mL.  However, the median 25vitD concentration was 67.9 ng/mL, which is well below the recommended sufficiency level of 100 ng/mL.


While dogs have been domesticated for thousands of years it is only recently we have confined them to a daily regimen of commercial dog food.  Vitamin D, which is not produced by sunlight in dogs, was historically obtained from eating the fat stores of killed prey.

In this study, more than 75% of all dogs were classified as insufficient.  Given the importance that 25vitD has on health status, dogs should be evaluated and supplemented if needed.


  1. Sharp, C., Selting, K., & Ringold, R. (2015). The effect of diet on serum 25-hydroxyvitamin D concentrations in dogs. BMC Research Notes BMC Res Notes.