Q: The pet food my dog, Sarge, eats is being recalled because it contains too much vitamin D. Since vitamin D is necessary for good health, how can too much be harmful? A: Several companies’ pet foods were recalled this year after they were found to contain toxic levels of vitamin D. Humans can manufacture vitamin D with the help of sunshine, but dogs can’t, so they must ingest vitamin D in their food. If they consume too much, the excess vitamin D is deposited in the body. Vitamin D is important because it raises calcium levels in the blood. Calcium is essential because, among other things, it makes the heart and other muscles contract. However, excess vitamin D raises calcium levels in the blood to abnormally high levels, a harmful and potentially lethal condition called hypercalcemia. Interestingly, some rodenticides contain high levels of vitamin D that kill by causing …