Bupa explains: “Pernicious anaemia is an autoimmune disease, caused by antibodies from your immune system attacking your own body tissue, which it mistakes as being foreign. This causes inflammation in the lining of your stomach.
“Normally, a protein known as intrinsic factor, which is made in your stomach, attaches to the vitamin B12 released from the food you have eaten and then carries the vitamin through your bowel wall into your blood.
“If you have pernicious anaemia, the stomach cells that produce intrinsic factor may be damaged, meaning vitamin B12 can no longer be absorbed and a deficiency develops, leading to anaemia.”