Light micrograph section through human stomach tissue showing pernicious anaemia of the stomach. This refers to an autoimmune condition that affects the stomach, which means that the immune system, the body's natural defence system that protects against illness and infection, attacks the body's healthy cells. This results in the body's inability to absorb vitamin B12. The exact cause of pernicious anaemia is unknown, but it's more common in women around 60 years and people with a family history of the condition.