Search this area of the site for 'ASAS Handbook' and it should show up.
I too remember the member from India who used vitamin D to treat his AS. I know it worked very well for him.
One thing to be aware of with studies is that you need to read them carefully. It appears to me that three of the studies you linked us to are the same case. And one of them doesn't refer to Vitamin D and AS, but Vitamin D and Rheumatoid. Two different diseases. That doesn't take away from the import of vitamin D in treating autoimmune disease, or the fact that a severe Vitamin D deficiency to the point of rickets could be misdiagnosed as AS. But that there is only one case documented and repeated in several articles does mean that there aren't that many documented cases ... in my experience that indicates something interesting to be watched and explored (especially if you suspect it has to do with you). It's not something on which to base a self-diagnosis.
Sorry if that's not what you want to hear, but I hope you take it in the spirit in which it's offered.
Warm hugs,
