It's not just vitamin D toxicity, it's also Calcium toxicity.

For example, vitamin D3 (Cholecalciferol) increases Calcium absorption by 5-10x fold.

Besides, Calcium (surprisingly) are toxic for human bodies as well, in excessive amounts, and accumulates with age in body tissues.

Btw, vitamin D3 (Cholecalciferol) are commonly used as rat poison.