Vitamin B12 or B9 (commonly called folate) deficiency anaemia occurs when a lack of vitamin B12 or folate causes the body to produce abnormally large red blood cells that can’t function properly.
Red blood cells carry oxygen around the body using a substance called haemoglobin.
Anaemia is the general term for having either fewer red blood cells than normal or having an abnormally low amount of haemoglobin in each red blood cell.
There are several different types of anaemia, and each one has a different cause. For example, iron deficiency anaemia, which occurs when the body doesn’t contain enough iron.