Vitamin D and bone—the search for the optimal dose

Since the discovery that cod liver oil cured rickets back in 1918, bone disease has been the hallmark of vitamin D deficiency. Still, hundreds year later, we do not know the optimal vitamin D intake or levels for our skeleton. As for most nutrients, the effects of vitamin D intake in the body follow a U-shaped pattern—with an increased risk of detrimental effects at both very low and very high intakes, with a broad range of intakes in between regarded safe and sufficient (1). What the thresholds for too little and too much should be for vitamin D, are still not clarified.