Of course a vitamin deficiency makes one vulnerable. By the very definition of what makes a vitamin a vitamin it's essential to consume to live.
But large doses of Vitamin D doesn't supercharge anything. Dumping gallons of gas on top of car engine doesn't make it go faster. Too much Vitamin D is toxic.
Understand the risks of too much vitamin D, including a toxic reaction.
www.mayoclinic.org
Vitamin D toxicity, also called hypervitaminosis D, is a rare but potentially serious condition that occurs when you have excessive amounts of vitamin D in your body.
Vitamin D toxicity is usually caused by large doses of vitamin D supplements — not by diet or sun exposure. That's because your body regulates the amount of vitamin D produced by sun exposure, and even fortified foods don't contain large amounts of vitamin D.