There's also this: http://ihateticks.me/2014/08/25/vdr-...ey-do-and-how/

At the end it links to a study on the subject, but it's behind a paywall. It seems from the little out there that I've now read that we just don't know enough about what the three mutations or polymorphisms mean. Does that sound right? I'm not an expert on this stuff, not even close. Perhaps Kiwi can say a thing or two. Here is the article we can't access btw: http://www.sciencedirect.com/science...78111904003075