An interesting set of videos from U.C.
The upshot is that unless you work outdoors you are likely defficient in Vitamin D and need to raise your intake or production. How much? Where prior medical advice was to never exceed 1000 iu, it looks like 4000 iu is about ideal.
(Don’t argue at me that that is too high, these are folks with Ph.D. and M.D. so take it up with them)
Various findings include things like 62% reduction in breast cancer and better prostate cancer outcomes too. Significant improvement in immune function (what got me watching) and improvements in calcium handling, and many more from M.S. to schizophrenia.
UVB makes vit-D with 280 to 310 nm or so being best.