Defining thresholds for vitamin D I

For decades, there has been a large amount of debate concerning the 25-hydroxyvitamin D thresholds used to define vitamin D deficiency and sufficiency, as well as optimal status. In this chapter, we discuss the arguments for the use of the 25 and 50 nmol/L cutoff points, as recommended by UK SACN (25 nmol/L), and the US/Canada IOM, EFSA, and Nordic countries (50 nmol/L). We critique the use of these thresholds and the approach used to define them. In addition, we discuss the issues with reaching 25(OH)D thresholds that apply to specific subpopulations and suggest that extra support for ensuring vitamin D health may be required for these groups. We end with a discussion of other issues surrounding definitions of thresholds for assessing vitamin D status.