A recent spate of published studies adds to the drumbeatof those researchers who argue that vitamin D deficiency and insufficiency are tied to poor health outcomes for a variety of conditions in a large proportion of the US population. But the nature of these studies, mainly retrospective analyses, makes it difficult for regulatory bodies or specialty societies to develop specific recommendations for raising the established levels for minimum vitamin D intake. These circumstances have left some physicians reluctant to aggressively diagnose and treat their patients for vitamin D insufficiency.