As there is a danger of dogs not getting enough Vitamin D, there's also risk of overdose. The below article details what can occur when someone follow's their vet's advice and purchases a Hills Science Diet product.
Hills has infiltrated the vet office environment; touting how they have done all sorts of studies and quality control. They begin by subsidizing vet school programs. Now there is proof that their food is not helping dogs, but killing them.
It is not enough to observe a dog on this diet with a dry coat, hot spots, runny eyes and over the top poor behavior. Most dog owners will take their dogs to the vet for meds to help solve the issue, instead of looking to the source - the food.
I beg dog owners to approach the health of their dog holistically. What you feed is what you get. How you train and how often you train is what you also get out of your dog.
Read this article (please) and make a wise choice for your dog's nutrition.