Since magnesium is required for the conversion of Vitamin D into its active form, it’s also true that taking Vitamin D may not raise Vitamin D blood levels in those who are magnesium deficient.
Magnesium is depleted when Vitamin D is converted into its active form in the blood – in other words, Magnesium is ‘required’ to convert Vitamin D into its active form. It works BOTH ways. Magnesium is not only depleted, but you will not convert Vitamin D unless you have enough Magnesium to facilitate the conversion. In many cases, where large doses of Vitamin D are consumed but the Vitamin D level does not rise, both the person deficient and their doctor believe that they are having Vitamin D absorption problems.