medication for vitamin b12 deficiencysymptoms of low vitamin b12 levelsvitamin b12 deficiency curelow b12 treatmentlow vitamin b12 and weight gainsymptoms of low b12 deficiencylow vitamin b12 symptomslow b12 neurological symptomssymptoms of low b12 and folatelow vitamin d and b12 symptomslow b12 dizzinesssymptoms of low b12 in elderly