Not to worry, the reference blood values for Vit-D are not derived from population averages, but from observational studies that show correlations between different levels and Vit-D deficiency syndromes. While there are differences of opinion about whether 30ng/ml or 50 ng/ml should be used as the defining threshold for "normal" i.e. sufficient, less than 20 ng/ml is generally considered the threshold below which supplementation should be considered.