 Inflammatory bowel disease is a chronic inflammatory condition of the intestine that includes Crohn's disease and ulcerative colitis. If you compare identical twins, even though they have the same genes, most of the time if one twin has it, the other does not. So there must be some important non-genetic trigger factors. What might they be? Well, studies like these offer the clue. Why do those living in the southern United States have lower IBD rates than those living in the north? Maybe it's because those living in the south get more sun, which means more vitamin D, which may mean less inflammation. So do those with Crohn's and ulcerative colitis with low vitamin D levels have worse disease? Apparently so, increased risk of surgery and hospitalization, and those that normalize their vitamin D levels appear to reduce their risk of relapse. But instead of better vitamin D leading to better Crohn's, maybe the better Crohn's led to better D. They felt so good they went outside more. You can't tell if it's cause and effect, unless you put it to the test. The first pilot study tried a thousand units of vitamin D a day and saw no change in the Crohn's disease activity index, though at six weeks there may have been a slight increase in the inflammatory bowel disease quality of life scores. But even that disappeared by year's end, pretty disappointing results. Maybe they didn't use enough? How about 1,200 a day? The relapse rate appeared to be cut in half, though there were too few people in the study to read statistical significance. How about 2,000 international units of vitamin D a day? Gut leakiness, so-called intestinal permeability, continued to worsen in the placebo group, appeared to stabilize in the vitamin D group. The only those who reached blood levels over 75 in animals per liter appeared to have a significant drop in inflammation. And indeed, if you start Crohn's patients on a thousand and then ramp it up until they reach a target blood level, you can get a significant boost in quality of life, accompanying a significant drop in disease activity. Disease scores under 150 are considered remission, so the majority of patients achieved remission, with improvements in disease activity and all but one patient. This suggests that Crohn's patients may want to take 5,000 international units of vitamin D a day, but that's nearly 10 times the RDA. Why so much? Because that's what it may take to get normal vitamin D levels, as in normal for our species levels. The kind of levels one might get running around half naked in Africa as we did for millions of years.