Forms and structure of vitamin D

All forms of vitamin D are secosteroids, sharing a close structural and functional resemblance to steroids. The full implications of a “vitamin” acting as a steroid has yet to be fully appreciated by many in the research community. The overlap between steroids and secosteroids is key to understanding the Marshall Pathogenesis. It explains how a “vitamin” can exert short-term palliative effects and long-term harm. Patients on the MP are advised to avoid consuming vitamin D, because of its immunomodulatory effects.

All forms of vitamin D belong to a family of lipids called secosteroids. Secosteroids are very similar in structure to steroids except that two of the B-ring carbon atoms of the typical four steroid rings are not joined, whereas in steroids they are.

The levels of each of the vitamin D metabolites are affected by a complex network of feedback mechanisms involving multiple enzymes and receptors, indicating vitamin D is regulated more like a steroid than a nutrient.

In the published literature, researchers sometimes distinguish between “steroid” and “secosteroid,” but not always.^{1 2}

This failure to discriminate is less an indication of sloppy research and more a testament to how vitamin D behaves. The vitamins D act very much like steroids, binding nuclear receptors and modulating the immune response. Not only that, there's growing evidence that vitamin D causes adverse side effects like chronic disease over the long term just like anabolic steroids and corticosteroids.