But don't start taking it without actually testing first. Hypervitaminosis D doesn't sound like any fun at all.

It feels uncomfortable to be advising Less Caution but in the case of vitamin D supplementation most people who don't supplement vitamin D already and who don't spend their lives naked in the sun would be well served just adding daily vitamin D3 to their schedule. The safety risk is negligible and for most people the value of information over assuming based on priors and just supplementing is low.