side effects of low b12 levelslow levels of vitamin b12 symptomssymptoms of low b12 levels in the bodylow b12 treatmentlow vitamin b12 and weight gainsymptoms of low b12 deficiencylow b12 neurological symptomssymptoms of low b12 and folatelow b12 dizzinesssymptoms of low b12 in elderlycause of low b12low vit b12 symptoms