SOURCE: Taylor CL, et al. Questions about vitamin D for primary care practice: Input from an NIH Conference. Am J Med 2015;128:1167-1170.

Clinicians continue to have well-founded uncertainties about how to best capture potential benefits of vitamin D. Although there is no doubt that vitamin D deficiency impairs skeletal health, the optimum application of vitamin D supplementation for otherwise healthy persons is ill-defined.

Fairly strong evidence supports vitamin D supplementation in frail seniors to prevent falls. Beyond that, there is little definitive evidence on which to rely. Observational studies indicate that low vitamin D status is associated with risk for cardiovascular disease, cancer, diabetes, and other important disorders, but whether this relationship is causal is not yet known, and whether correction of such a causal relationship (if established) will improve outcomes remains to be determined.

The NIH conference confirmed that 25(OH) vitamin D remains the preferred metric, while acknowledging that consensus does not exist to specifically define optimum vitamin D levels or a specific threshold indicative of deficiency. Equally confounding is the acknowledgement that methods for measuring 25(OH) vitamin D are not standardized and may vary from laboratory to laboratory by as much as 20%.

Currently recommended supplemental doses of vitamin D (400-1000 IU/d) are generally considered safe, but concern for toxicity was expressed in reference to mega-dosing (10,000-50,000 IU/d).