What is vitamin D insufficiency? And does it matter?

The term nutrient "insufficiency," as commonly used, refers to a nutritional status intermediate between classical, severe deficiency, and full normal. As both "deficiency" and "insufficiency" are causes of dysfunction and disease, there is no biological basis for a distinction between them. What is important to note is that, in the case of vitamin D, the preponderance of the evidence indicates that there is real, preventable disease in the range of vitamin D status values now labeled "insufficient."