have you checked out the zinc connection, need?
if not, here is some info:
i used to have low D3 and asked the hospital how to get my level up 50nmol/L fast. they said take 50,000IU per day x 10 days. i did so and my level went from low 70s to 149.
later i realized i was zinc deficient (ie 8.6 umol/L, normal range is 10-20, some sources say 11.5-18.5, and in the literature healthy controls sit in a tight average around 18.2 umol/L).
when i was zinc replete i got a d3 test of 103 nmol/L. i wanted to be closer to 150 so i decided to do 50,000IU d3 per day x 8 days. my followup d3 level was 271 nmol/L.
so my dose response basically tripled.
weight loss is a symptom of zinc deficiency, and zinc is known to be low in ms patients.
zinc is involved in over 300 process in the human body, so if it is involved in your low d3 levels, it could be affecting quite a number of other things you would not think were connected.
for instance my low uric acid level, which was stuck at or below the ms average for years, suddenly bounced up to the levels seen in healthy controls, after i corrected my zinc deficiency.
world's healthiest zinc foods:
certain drugs and foods impair zinc absorption, such as bread for example (gluten grains in general). phytates are also a problem for zinc absorption.
i saw one study where they took celiac patients and healthy controls and put both groups on a gluten free diet. serum zinc levels increased in both patients and controls.
what's your diet and supplementation and medication regimen like? there might be some clues there. for my part, prior to dx i had very little bioavailable zinc in my diet, and at the same time, ate plenty of foods that would impair zinc absorption. recipe for disaster!