Health is better at serum 25(OH)D above 30ng/mL.

There is clear evidence of health benefit in studies raising serum 25(OH)D in the range of 20-50ng/mL. However, the results have not been consistent. The likely reasons include the intrinsic smallness of nutrient effects, as well as failure of trial designers to give adequate attention to starting vitamin D status and to adequacy of dose. Similarly, systematic reviews have also usually failed to use dose or starting level as criteria for study inclusion. The result is null studies, on the one hand, and, on the other, meta-analytic aggregate effects that are artifactually minimized. At a more fundamental level, the issue with vitamin D (as with most nutrients) is not the demonstration of efficacy but the defining of intake. Randomized controlled trials are poorly suited to answer such a quantitative question. Alternative approaches to defining nutrient requirements based on physiological grounds are needed (and possible). Alternatively, requirements can be based on a calculus of harm, recognizing that any selected level carries two risks: possible benefits foregone and possible harm risked. The decision should be for the nutrient status level that minimizes those inescapable risks. This article is part of a Special Issue entitled 'Vitamin D workshop'.