 The Institute of Medicine raised their vitamin D recommendations based on a blood level target of 20 to prevent bone softening disorders, such as rickets. Although the Institute's target of 20 may prevent the overt skeletal deformities associated with rickets, there is now, according to a review last year, overwhelming and compelling data suggesting that the human body requires a blood level of above 30 nanograms per milliliter for maximum health. Dr. Hock bases this assertion on data like this, a graph not of rickets' risk, but of colon cancer risk, versus vitamin D levels, suggesting that the Institute of Medicine's 20 is good, but 30 or more may be even better if you're considering vitamin D from the cancer prevention angle instead of just strictly skeletal health. There are similar graphs for breast cancer risk, multiple sclerosis, and other conditions linked to vitamin D status. Instead of going through each, let's just jump straight to total mortality. What blood level of vitamin D will enable us to, on average, live longest? Here's the graph, and as you can see, it's kind of a U-shaped curve, not having enough in our bloodstream associated with higher mortality, but it looks like we can have too much as well. So what's the sweet spot in the middle, the lowest mortality risk? This is the Institute of Medicine's recommendation, 20 nanograms per milliliter, which translates to the 50 nanomoles per liter. You see here, here's 30, and this is 40. So for longevity, around 30 would seem a better target. So one strategy to arrive at a vitamin D recommendation would be to figure out how much sun and or supplements we might need to take to get our levels to 30.