Blood types have previously been linked to a variety of medical conditions, from influencing heart disease risk to thinking and memory problems. Now, some new research, published in the Brain Research Bulletin, may have revealed the role that your blood type plays in the chance of developing cognitive diseases such as Alzheimer’s.

The study, carried out by researchers at the University of Sheffield, looked at the amount of grey matter, a type of nervous sytem tissue, in people’s brains and then compared this with their blood type. They found that those with blood type ‘O’ had more grey matter than those with any of the other three types. A greater volume of grey matter has been previously linked to protection against diseases like Alzheimer’s.

The participants involved in the study were mentally healthy adults who had previously undergone MRI scans for other research. After collecting details on their blood type, the scientists began examining their brain data to look for any apparent associations. What they found was that people with types ‘A,’ ‘B,’ and ‘AB’ had smaller amounts of grey matter in the posterior portion of the cerebellum—the back of our “little brain.”

“What we know today is that a significant difference in volumes exists, and our findings confirm established clinical observations,” explained Professor Annalena Venneri, co-author of the study. “In all likelihood the biology of blood types influences the development of the nervous system. We now have to understand how and why this occurs.”

As people age, the volume of grey matter decreases. Some of the earliest parts of the brain damaged by Alzheimer’s are the “temporal and limbic” areas of the brain, both of which are also towards the back of the organ. The study found that these were also smaller in those with blood types ‘A,’ ‘B,’ and ‘AB.’

“The findings seem to indicate that people who have an 'O' blood type are more protected against the diseases in which volumetric reduction is seen in temporal and mediotemporal regions of the brain like with Alzheimer's disease for instance,” said Matteo DeMarco, the other author of the paper. “However additional tests and further research are required as other biological mechanisms might be involved.”