For the majority of the population with A, B, or O blood, this particular risk appears significantly lower — though the research does not suggest AB-type individuals will inevitably develop dementia.
Gastric cancer and ulcers: opposite risks for type A and type O
Gastric cancer is the 5th most diagnosed cancer and the 3rd leading cause of cancer-related death worldwide. Among blood types, individuals with type A blood are described as facing the highest risk of developing it, likely because H. pylori infections — a bacterium that causes stomach inflammation and ulcers — are more prevalent in type A individuals.
People with type B and AB blood are also said to carry a greater risk of gastric cancer than type O individuals, though the association is strongest for type A.
Type O blood, however, is not without its own documented vulnerabilities. Studies show that type O individuals face a higher risk of peptic and duodenal ulcers compared to other groups, attributed to an enhanced binding of Helicobacter pylori to epithelial cells in the stomach lining. Peptic ulcers are painful open sores that develop in the stomach and upper intestine — a distinct but serious condition from cancer.
The studies referenced here reflect associations identified in research to date, not established clinical guidelines — and several mechanisms, including the exact pathway between AB blood type and dementia, remain under investigation. As epidemiological research on blood type and disease risk continues to develop, the open question is whether these associations will eventually translate into blood-type-specific screening protocols or preventive recommendations in mainstream clinical practice.
