My vit d lvl is 20 ng/ml. My doctor says suppliments. It appears linked to many diseases - but is defiency a cause or effect? Should I look deeper?

Vitamin D levels. The only place you need to look is on your local pharmacy or health food store shelves. I live in hawaii, the land of sunshine and palm trees, and I routinely screen for vitamin d deficiencies and am no longer amazed at how many patients in the land of sun are deficient. I have no idea why. You need to take however much vitamin d supplements that will increase your level to 80 to 100 ng/ml.