As much as 90% of the US population may be deficient in vitamin D, so you have a good chance of it. That said, I agree that testing is good, either before or af

As much as 90% of the US population may be deficient in vitamin D, so you have a good chance of it. That said, I agree that testing is good, either before or after supplementation. https://www.grassrootshealth.net/document/grassrootshealth-participants-compare-general-u-s-population/ https://www.grassrootshealth.net/document/grassrootshealth-p...