There is no harm in exceeding the recommended amounts or using more than one option. What happens if you do not get enough vitamin B12? A mild deficiency may cause no symptoms at first. If untreated, the typical deficiency symptoms in adults include loss of energy, tingling, numbness, reduced sensitivity to pain or pressure, blurred vision, abnormal gait, sore tongue, and mental problems like depression, memory loss, and personality changes. Signs of a B12 deficiency may take months or years to emerge, and they are usually reversible on the administration of B12. If you suspect you have a deficiency, you should get a diagnosis from a medical practitioner, because each of the named symptoms can also be caused by problems other than a B12 deficiency.