I tested low for Vitamin D a couple of years ago, and the doctor put me on 50,000 once a week for a month. That brought me up to the lowest end of normal.
She didn't say a thing about the benefits of taking it other than bone health.
Last year, another doctor said I was supposed to keep taking it as a daily supplement (whatever the usual daily dose is). She retested me and I was still just barely in the normal range.
I have it, and I'm going to take it right now.