Vitamin D deficient people usually have other deficiencies as well, pinning it down to D is textbook causation-correlation mixup. As TFA says, it "may" account

Vitamin D deficient people usually have other deficiencies as well, pinning it down to D is textbook causation-correlation mixup. As TFA says, it "may" account for it. Or may not. You need a control group with D (but no other) deficiency to upgrade from "may" to "does".