Vitamin B12 deficiency can occur in a number of ways.
In the long term, B12 deficiency can also cause severe neurological deficits. These affect the spinal cord (complicated spinal cord with subacute degeneration), the surrounding nerves or the brain (dementia). As a result, there may be many types of symptoms: paresthesia, burning limbs, instability and muscle weakness, cognitive problems, etc.
Complete lack of B12 can lead to megaloblastic anemia, which is a special picture of anemia in which red blood cells are larger than normal people due to production difficulties. The picture is characteristic at the laboratory level, but in patients it may be difficult, tired and pale (like other anemias).
At first it had no symptoms, which meant that the only way to find out was to measure vitamin B12 in the blood, a common laboratory test.