What is the optimal level of vitamin D? - separating the evidence from the rhetoric

Vitamin D deficiency is thought to be common in Australia. It is unclear when vitamin D supplementation should be prescribed.

We assess the evidence that guides clinical decision-making on supplementation with vitamin D following a vitamin D test result.

Vitamin D assays are inconsistent and inaccurate and there is weak evidence around the level of 25-hydroxyvitamin D (25(OH)D) that is optimal. Evidence of links between vitamin D deficiency and disease come from observational studies and there is little support from randomised controlled trials of vitamin D supplementation. Where there is evidence of a link, increased risk is largely confined to very low 25(OH)D levels, with minimal health gains for 25(OH)D levels greater than 50 nmol/L. New evidence indicates that both high and low 25(OH)D levels may be associated with increased health risks. Taken together these considerations present a considerable challenge to clinical decision-making around treatment on the basis of 25(OH)D levels.