I found a video of a medical school lecture on Vitamin D. It has lots of good information. When I am allowed to post links I’ll come back and post it for others to see. The Doctor’s lecture was very fast-paced and full of technical terms but also understandable to non doctors too. He spoke a lot about deficiencies being more common than realized, and also about how the recommended levels really need to be raised.

    

So do you guys ever worry about Vitamin D toxicity? Because you do know that there are consequences to having too much Vitamin D.

That information I posted about earlier goes into depth about toxicity of vitamin D too.
One of the things mentioned in that lecture was that after sunlight exposure (not to the point of a sunburn, though), your skin can make the equivalent of 10,000-20,000 units of vitamin D. So, most of our vitamin D requirement comes from sun exposure.
I know my levels of vitamin D were low because I was rarely outside, and didn’t eat enough foods containing Vit D. I will be having my Vit D levels tested by my Doctor during my next visit to see if my levels have increased to where they should be.