**4. Optimal levels of 25(OH)D3**

The molecule used to assess vitamin D sufficiency in a population is 25(OH)D3 [9]. It appears that vitamin D has physiologic effects beyond those related to bone physiology and mineral homeostasis. It may be that the alarming prevalence of vitamin D deficiency observed all over the globe may be contributing to the development of autoimmune diseases. Based on bone-related biomarkers such as intact parathyroid hormone, calcium absorption, and bone mineral density, maintaining a 25(OH)D3 level of at least 32 ng/ml appears sufficient.
