Deficiency of vitamin B12 can be slow to develop, allowing symptoms to gradually emerge and worsen over time. It can come on relatively easily as well. Despite the number of signs that a vitamin B12 deficiency can cause, it is easy to miss or mistake the disorder with something else. Symptoms of vitamin B12deficiency can include: Strange feelings in your hands, thighs, or feet, numbness, or tingling Trouble walking (staggering, balance problems) anemia Inflamed, swollen tongue Thought and reasoning problems (cognitive difficulties), or memory loss Weakness Tiredness