Is deficiency of vitamin b12 affects metabolism and if yes then how it affects?

B12 Deficiency: A deficiency of vitamin B12 can lead to vitamin B12 deficiency anemia. A mild deficiency may cause only mild, if any, symptoms. But as the anemia worsens it may causes symptoms such as: weakness, tiredness or light-headedness rapid heartbeat and breathing, pale skin, sore tongue, easy bruising or bleeding, including bleeding gums, stomach upset and weight loss, diarrhea or constipation, .