[deweller]

"Just" focusing on one nutrient isn't the answer. But sufficient Vitamin D is important. It is something we should pay attention to.

Health is complex. No one is advocating ignoring all the other aspects of immune system function by paying attention to vitamin D.

[Update] I see you have toned down your comment since I started composing this response. We are in agreement.

[billman]

I think it's important to note that Vitamin D is a hormone. And the body produces it as well.