Vitamin D supplementation is also sketchy and hotly debated topic in. Everyone agrees that it is important, but the currently accepted lower limit and whether you need to supplement if you are below is disputed. That limit was set based on extrapolating observations that were not fully controlled. So that limit has limitations basically. If you are healthy you shouldn’t bother with vit D suppl. If you have health concerns please do, but from a reliable source/brand. Supplements are not regulated.