Hello there
Well did you do any diagnostic test to say that you have low vit d and
b12 levels?
Also muscle strength is not really related to low b12 levels....
It is important to know your height,weight and activity levels you are engaged in.
Do get back with answers for proper guidance.
Regards
Next Steps
Dr.Raviraj Francis
MPTh(Rehab),MPT(MSk).UK