Hi Bob:  Has your wife had her vitamin D levels checked to see where she stands with this issue.  I think having this info would help to determine if she is deficient or at optimal levels of D.  This test is a very simple blood test, and is called 25(OH)D. If she were at a deficient level that would tell you how much additional D3 would be necessary for someone living above the 35th parallel.    Here's a good link explaning this issue from the Canadian Family Physicians Org. on D3.  I don't know if supplementation of Calcium, and D3 alone would reverse her osteoporosis; usually it requires an additional drug, but who knows it may be possible to revert her scores with supplementation and sun alone, but I wouldn't completely count on that.   You mentioned Human Growth Hormone, is that what the Dr wanted to try or could it have been daily injections of Forteo which is recombinant human parathyroid hormone, given for 2 years?  I took Forteo and did really well on it, but it's ususally rx'd for those with relatively low t-scores at apprx less than -3.0.  Some Drs will rx it at -2.5 with existing or previous fractures.   If your biggest issue is not using bone meds, or that you would prefer something more natural, have you looked into Fosteum?  Here's a link on Fosteum if you aren't familiar with it.   I haven't found any particular studies about your hypothesis of moving to a location that has greater sun exposure year round for osteoporosis.  I live in an area with plenty of sunshine (CA Desert) but I still have a low reading on D in spite of the fact that we get sun most everyday.  I spend at least 15 minutes, several times a week or more, in the sun without sunscreen and take some D3 but remain below the optimal level.  This is probably due to a mineral metabolism problem that I have, but you need to take other things into consideration when you are trying to raise someones Calcium and D levels.   If I find any studies that answer your question I'll repost it, but in the mean time read the link above which should give you a very good base of info on D3 exposure, how to obtain it and also maintain it throughout the winter months when sunshine is limited or non-existent.  The additional graphs within the link, and included studies and charts are very helpful in understanding the mechanism of D.   Good luck and do you know her t-scores, if so that would help to answer this question better.