Interesting topic. I get a bloods MBA plus extras done every 6 months, roughly January and July (winter down under). So last January my Doc sends me off for skin cancer scan and get some pre cancer squamous cells burnt off both ears. Catch a few less rays to let that heal. July test, your vitamin D is low, start taking a daily or weekly dose. I do, mostly. Now the sun is heading back this way, I get more sun with my morning coffee.
I still take the vitamin D when I remember, safe in the knowledge, I think, that the body absorbs what it needs and pisses away the excess. No chance of od'ing on Vitamin D then.
And to be very clear, my Doc did NOT say it would reduce my risk of cancer or heart disease. As for cognitive decline she said said the impact of the '70s is irreversible, get outta here boomer.