I don’t know too much about it except that it’s an autoimmune disease and has a complex, multi-causal etiology and pathology. In my reading on autoimmune diseases in general there seems to be a direct link between latitude an incidence. Specifically, the farther from the equator you live the more likely you are to get Crohn’s, Type 1 diabetes, rheumatoid arthritis, and so on.
This being our wont in Western society, we try to isolate it down to a single cause: farther from the equator means less sunlight, which means vitamin D deficiency, so it must be vitamin D. So we try to feed people vitamin D, but this doesn’t cure the condition since it’s notoriously hard for your body to get utility from vitamin D supplements (and in fact it’s easily toxic) and even hard to get enough in food. Plus there’s the issue that maybe it’s not just the vitamin D itself but some combination of biochemistry that happens when you expose yourself to sunlight (the main way humans have gotten a majority of their vitamin D throughout history). But wait, what about skin cancer? Let’s put on sunscreen and go outside for 15 minutes a day. Nope. Sunscreen blocks vitamin D production. Plus in northern climates it’s very hard to get enough sunlight to produce enough vitamin D, especially in the winter months. A number of studies suggest that over half of Americans are deficient.
My guess is that vitamin D is not the issue, but more generally sunlight is. Or more precisely, given your ethnic background, there’s a range for optimally healthy sunlight exposure, and if you go too far out of that range in one direction or the other, you end up with health problems. Autoimmune and other disease on one end, cancer and poor skin health on the other. But I doubt it’s even that simple because lifestyle in general can predispose you or provide resilience — diet, exercise, exposure to environmental insults, and patterns of activity that affect emotional and mental state.
One thing that I think is overblown is the portion of the equation that is genetically predetermined. The pendulum in science has swung too far towards genetics in terms of explanation in general, and this completely contradicts the evidence.
If I were diagnosed with Crohn’s or any other autoimmune condition, here’s what I would do personally. First, devote several hours a day to physical fitness and conditioning, as if I were a professional athlete. Second, experiment with diet like a mad scientist: try every supposed “good health” diet out there, but mixing it up and listening to my body and mental state. Third, I would experiment with daily sunlight exposure, using guidelines based on my natural skin tone (darker = need more sun). Next, I would examine my interpersonal relationships and eliminate/reduce contact with anyone who I even suspected of being a “net negative” emotionally in my life. Finally, if I didn’t see dramatic results, I would move closer to the equator and to a locale that’s very different from my current one (different culture, different daily patterns, etc), and change up my daily routine, esp. if I spent more than a few hours a time doing the same thing (like staring at a computer screen).