As a data point, I underwent cancer treatment a few years ago in the US at Massachusetts Eye and Ear and there high-ish dose vitamin D (can't remember the actua

As a data point, I underwent cancer treatment a few years ago in the US at Massachusetts Eye and Ear and there high-ish dose vitamin D (can't remember the actual dosage) was encouraged, though it wasn't part of the treatment they provided. The doctors and other staff all seemed to take it vitamin D as a preventative measure as well.