I’m not sure about optimal, but normal depends on age. 600 ng/dL would be a reasonable average for a normal level. https://www.mayocliniclabs.com/test-catalog/

I’m not sure about optimal, but normal depends on age. 600 ng/dL would be a reasonable average for a normal level. https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/83686 https://www.mayocliniclabs.com/test-catalog/Clinical+and+Int...