Quite on the contrary, scientific research is still severely lacking. There's even no sound scientific consensus on vitamin d's rda. How should we acquire it,

Quite on the contrary, scientific research is still severely lacking. There's even no sound scientific consensus on vitamin d's rda. How should we acquire it, by sunbathing or by supplementing, in a high dosis bolus or a daily small amount, there are endless unanswered questions and endless unposed questions. You rightfully mention a high correlation with other metrics that make, in my opinion, vitamin d health benefits and health disadvantages scientifically impenetrable. As a tiny datapoint, I refer to the research of the (on hn at least) highly acclaimed Dr. Rhonda Patrick, who states that 70% of Americans are currently deficient on vitD. She also states that vitD has effects on 5% of gene expression, and is very important in the brain formation of foetuses since it assists the production of serotonin. If anything, and despite of admittedly huge efforts already, vitD is heavily underresearched and many of its mechanisms unexplored.