Mastering Nutrition
Short answer: 25(OH)D is 1000 times weaker at activating the VDR than 1,25(OH)D, but 1000 times more abundant. This is why I advocate measuring both, and ultimately believe we need to create a calculated index of "biological vitamin D activity" from them.
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This snippet is from the April 13, 2022 AMA. The full recording and transcript is reserved for Masterpass members. Here is a preview of what's included:
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Chris Masterjohn, PhD, is the Founder and Scientific Director of the mitochondria test Mitome.