Can't speak to the general point, but for COVID-19 in particular, it's starting to look like this matters. And not surprisingly, we're all kind of obsessing on that. If something so simple can keep people off ventilators, it's surely worth pursuing.

Past that, someone I know who lived in Alaska a few years started developing weird symptoms, including a declining ability to balance. Turned out she had low D, and once she fixed that, the symptoms all went away.