2. Weakness and Fatigue
If you have low levels of Vitamin B12, you will feel less energized. This is why you are feeling weak and fatigued. The reason behind this is because your body is not able to produce enough red blood cells that are responsible for distributing oxygen to all parts of your body.
This is what usually happens to people suffering from pernicious anemia, a type of autoimmune condition. Those who have this condition will not be able to produce enough intrinsic factor, which is an important protein. This protein is the key to preventing B12 deficiency as it binds with the vitamin B12 in your gut in order for your body to easily absorb it.