 Figuring out what level of vitamin D supplementation is necessary to bring one's level up to the specific blood level, like 30 nanograms per milliliter, the level associated with the longest lifespan, is not as easy as one might think. For example, here's seven people, starting out with blood levels under the target of 30. They all got the exact same dose of vitamin D, 1,600 units a day. And here's what happened to their levels over the next six months. One person's blood levels tripled, another even quadrupled. But in these three, even though they were all in the same dose, their blood levels hardly moved at all and stayed under 30. So let's say you're trying to come up with a recommendation for people. Here's a scatterplot of about 3,000 people, blood level versus intake. So people taking 10,000 a day, average about, you know, blood level about 75, with 95% of people falling in between about 40 and 110. If we want to choose a dose for which 95% of people reach the target of 30, we'd probably choose around, you know, 6,000 a day. But though that would get most to the minimum, the average level would be over 50, which is higher than we'd like to see on the U-shaped vitamin D total mortality graph. That's equivalent to like 125 nanomoles per liter, which is off to the right of the graph. You can see why forming dietary recommendations is a formidable and unenviable task.