For many years neurologists have treated MS patients with high doses of Vit. D to curtail the symptoms.    As a nurse, I routinely see our MS patients at what is referred to as toxic levels.  Over 100 to 120. It is true that few doctors know how to treat Vit. D deficiency.  Being a previous gastric bypass pt. from 2003, doctors were unaware that all bypass pts. would be vitamin D deficient.  Yes they would check the Vit. D. level and maybe for 6 weeks give the vitamin in large doses then have you stop.  Three years after my bypass, my WBC (immune system) went down to 3.0.   None of the doctors contacted, even in large teaching hospitals were aware of anything that could be causing my lowered immune system.  Four years later I was diagnosed with Lymphoma at the age of 60.  Went through chemo, and the entire time questioning my oncologist about the causes of my type of lymphoma.  No one knew.  After treatment I became sicker and my WBC went down to 3.0.  Had two major infections and missed more work then when I was receiving chemo.  I asked my computer the names of all the Vitamins and minerals that pertained to the immune system.  I was then checked for any def.  The Def. was Vitamin D. My oncologist didn't know how to treat my deficiency.  Going back to the bypass clinic I have worked with a nurse practitioner and one of the surgeons proving by labs that Vit D is infact one of the major components of the immune system. My labs have been drawn every two months for the past 18 months.  As the Vit D level rises so does my WBC.  In one and l/2 months on large doses of Vit. D, I felt better then I had in years.  I maintain my level at high 60s.  Feel great and for 11 months have worked 4 days a week, 12 hr. shifts, on midnights at the age of 63 yrs. young.  My Lymphoma was high grade, and after 21 months from the last chemo treatment I remain in good remission.   Please read more about what Vit. D actually does and how it can prevent many cancers.  Mayo clinic did a study on Lymphoma pts. and found that Vit. D. treatment during your chemo could double your life expectancy.  One of our new diabetic clinics is now treating type I diabetics with large doses of Vitamin D.  You must have your Vitamin D level checked frequently until your doctor has determined what dose you must take to maintain an adequate vit. d level.  This really is important for many vitamins and minerals.   When I first suspected Vit. D. was the cause of wiping out my immune system I said to my oncologist, please don't tell me a simple vitamin could have kept me from getting this cancer. The only thing my oncologist could say to me is I'm sorry I didn't listen to you.  I have been horrified to find many gastric bypass pts. from other hospitals and areas of the country who have never been put on any kind of vitamin supplements.  Malabsorption is one of the things that allows you to loose weight so fast, it goes right through the body.  In fact everything goes right through, and vitamins and minerals and medications do not absorb properly.  Any person that has difficulty with malabsorption in the intestines and colon will have the same problem of Vit. D. deficiency.   Hope this has helped.