Had breast cancer 3 1/2 years ago. My vitamin D test showed 29 at that time. Since I have been taking vitamin D and 6 months ago my level had gone up to 40. Just had a test and it is back down to 27. I just upped my vitamin D 3 months ago to 4,000 a day. I was at 2,000. Could this mean my cancer is back or do I need to up my intake to 6,000? What can cause it to drop?