Overview of the conference "Vitamin D and Health in the 21st Century: an Update".

We summarize the key findings, strength of the evidence, and research needs identified in the National Institutes of Health conference "Vitamin D and Health in the 21st Century: an Update," which was held in September 2007; a systematic evidence-based review; and a National Institutes of Health roundtable discussion held after the conference by scientists with relevant expertise. The evidence-based review addressed 5 questions on 25-hydroxyvitamin D [25(OH)D] and functional outcomes across the life cycle and response to exposure, bone health outcomes of supplementation, risks and benefits of sun exposure, and adverse outcomes. These questions also framed the conference and roundtable discussions. Researchers have made considerable progress in understanding the relation of 25(OH)D to bone health outcomes in the elderly and in postmenopausal women, but we know less about its impact on other stages of the life cycle and in racial and ethnic groups. Limitations of the existing data include the failure of many studies to control for important confounders [baseline 25(OH)D concentration, skin pigmentation, body mass index, compliance, etc], sparse data on key vulnerable populations (dark-skinned persons, reproducing women, infants, children, and adolescents), problems of accuracy and excessive variability in measuring 25(OH)D, lack of established relation of 25(OH)D with functional outcomes except in the elderly, and limited information on the effects of vitamin D independent of calcium, magnesium, and phosphate. Future research should determine and validate across the life cycle relevant functional outcomes for bone and other health factors as well as adverse outcomes for the biomarker of exposure, 25(OH)D, to enable assessment of the role of vitamin D status in health maintenance and disease prevention.