Strange Sensations of Pins and Needles
One of the more serious side effects of a long-term B12 deficiency is nerve damage.
This can occur over time, as vitamin B12 is an important contributor to the metabolic pathway that produces the fatty substance myelin, which surrounds your nerves as a form of protection and insulation.
Without B12, myelin is produced differently, and your nervous system isn’t able to function properly. The result is a strange feeling of pins and needles especially in your hands and feet.