London, June 4 (IANS): People with an 'O' blood type have more grey matter in their brain, which helps to protect against Alzheimer, than those with 'A', 'B' or 'AB' blood types, new research has found.

The results suggest that blood types play a role in the development of the nervous system and may cause a higher risk of developing cognitive decline.

As we age, reduction of grey matter volumes is normally seen in the brain, but later in life this grey matter difference between blood types will intensify as a consequence of ageing.

"The findings seem to indicate that people with an 'O' blood type are more protected against the diseases in which volumetric reduction is seen in temporal and medial temporal regions of the brain such as with Alzheimer's disease for instance," said one of the researchers Matteo De Marco from University of Sheffield in Britain.

The researchers analysed the results of 189 Magnetic Resonance Imaging (MRI) scans from healthy volunteers.

They calculated the volumes of grey matter within the brain and explored the differences between different blood types.

Individuals with an 'O' blood type have more grey matter in the posterior proportion of the cerebellum, the results showed.

In comparison, those with 'A', 'B' or 'AB' blood types had smaller grey matter volumes in temporal and limbic regions of the brain, including the left hippocampus, which is one of the earliest part of the brain damaged by Alzheimer's disease.

The study was published in the journal The Brain Research Bulletin.