Vit D levels are very hard to rise with sun only. You need to be at certain time of the day (around 12pm) to be full body naked for 20-30min to get a special ray diapason that is beneficial for Vit D increase. Every day and for a long time. That is why even living in Cali or Florida does not make much difference. When studies were done, the further from Equator people are, the more cancer they have, provided all other food/environmental conditions are the same.
For the cancer patients the levels, to the best of my knowledge, must be from 80 to 100 ng/ml. I did not read the bibliography that Maia included, just my personal experience/reading. I know that when I stop taking Vit D, I have a drop down to 40, but normally it is in 80's with a maintenance dose. And I do live on Equator.
11/2005 CC stage 1, F,50yo@dx
Mod dif adenocar, MSS, APC, TP53, CEAs1.6-4.8
1/12 1met liver@Vena Cava, RFA, 3oxi,11 5FU
8/13 2 mets same place,SBRT
4/14 2 Xeliri+Avastin
5/14 Nano Knife liver same 2 mets
6/14 2 Xeliri, ADAPT
4/15 PET, 2 same mets,Cryo Liver
5/15 MJ Oil, Herbs, Suppl, ADAPT
10/15 PET, same area, doubled in size, high SUV
10/15 RH, HAI, visceral involv., no LN
2/16 red FF, 50% red dose FUDR, CEA trends up
3/16 CT, PET, MRI L.Lobe all in small tumors
4/16 No acceptable options, going home