Only 1,25-hydroxyvitamin D is useful for inborn and acquired disorders in calcium and vitamin D metabolism. It's often normal or even elevated in a vitamin D-deficient state because of secondary hyperparathyroidism. The active form of vitamin D gives you no insight into your vitamin D status. It's the major circulating form of vitamin D and it's used worldwide by doctors to measure the vitamin D status of patients. The only one to measure is 25-hydroxyvitamin D. Holick: I don't think there's any debate about this. I'd love to get both of your comments on what is the best biomarker to measure vitamin D levels. Taub: One of the things that has come up in many of these clinical trials is the biomarker by which we measure vitamin D. As a result, there are a multitude of association studies that have related vitamin D deficiency with increased risk for autoimmune disorders like type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, and increased risk for cardiovascular disease, neurocognitive dysfunction, infectious diseases, and some malignancies. We think that it does it for the purpose of regulating cellular growth and a variety of genes. Then we began to realize that basically every tissue and cell in your body has a vitamin D receptor, and the obvious question is, why would they be there? There's now a large amount of evidence to suggest that immune cells, colon, breast, skin, and other cells in your body can activate vitamin D locally. Therefore, looking at receptors for 1,25-dihydroxyvitamin D, they were found in the intestine, bone, and kidney, which regulate calcium metabolism. Originally, we realized that vitamin D is really important for your bone health. We're now recognizing that vitamin D, of course, has to get activated, like you said, first in your liver to 25-hydroxyvitamin D and then in your kidneys to 1,25-dihydroxyvitamin D. You have shown throughout your career that vitamin D has a variety of health benefits, ranging from being anti-cancer to improving blood sugar, to enhancing immune response. I'm going to start by asking Dr Holick a question. It's a pleasure to have you both here, and I'm looking forward to a very lively discussion.
She's been involved in many landmark clinical trials that have changed our clinical practice, including the Nurses' Health Study, the Women's Health Initiative, and most recently, the VITamin D and OmegA-3 TriaL (VITAL study). Over the past four decades, he's led many of the studies demonstrating the benefits of vitamin D and is responsible for bringing vitamin D to the radar of healthcare professionals.ĭr JoAnn Manson is another luminary in the field and a professor of medicine at Harvard Medical School. He was the first to identify the major circulating form of vitamin D in human blood as 25-hydroxyvitamin D3. They're both world experts on vitamin D.ĭr Holick is a pioneer in the space and a professor of medicine at Boston University. I'm really delighted to have Dr Michael Holick and Dr JoAnn Manson join us today. I'm a cardiologist and professor of medicine at UC San Diego. This transcript has been edited for clarity.
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