Not every one has the same symptoms of vitamin B12 deficiency. You and your best friend may both be low in vitamin B12, but have very different symptoms. Because the symptoms of low vitamin B12 vary so greatly the medical community has often concentrated on one symptom and ignored others. The result is that many people with severe symptoms of low B12 do not get treatment because they don’t have the symptom popular on a given day, the “symptom d’jour” you might say.
New research showed nearly 20 percent of those taking metformin had borderline low vitamin B12 levels which lead to vitamin B12 deficiency. http://articles.mercola.com/sites/articles/archive/2016/03/30/vitamin-b12-deficiency-metformin.aspx
Top 10 Foods Highest in Vitamin B12 (Cobalamin) Important info for vegetarians or those cutting back on animal protein, deficiencies may lead to fatigue, deficiency, anemia, mania or even damage to brain and central nervous system.