Catherine Bolshakov, of Dunedin, asks :-

Are people of certain blood groups more predisposed to various types of cancer?

Ian Morison, a haematologist at the University of Otago, responded.

Surprisingly the answer is yes. The difference is small but people with blood group A are approximately 10% more likely to be diagnosed with cancer compared with those with blood group O. Analysis of more than 100 studies involving more than 100,000 cancer patients shows this consistent but small increase in the rate of cancer.

Blood groups are created by carbohydrate-modified proteins that are present on the surface of red blood cells and also on numerous other tissues throughout the body. In New Zealand approximately 50% of people have blood group O, 40% are group A, and the rest are B or AB.

There are several theories about the reason for the increase in cancer in group A. One theory relates to different effects of these blood group proteins on cell behaviours such as movement and their resistance to the immune system and to cell death signals.

Other scientists point to the different levels of inflammatory proteins that are associated with different blood groups. Long-term inflammation of some organs can be linked to cancer development, and the blood group might affect this process.

Another theory relates to the role of the immune system in attacking cancers. Blood group proteins are associated with very strong antibody responses, which is why it is essential to match blood carefully before transfusion. Since some cancer cells display proteins on their surface that resemble blood group A proteins, the immune system of someone with blood group A may be less likely attack and destroy these cancer cells because they look like their own normal cells.

Another theory is that the clotting protein Von Willebrand Factor plays a role. People with blood group O have 25% lower levels of this blood protein which can modify cancer-related factors such as cell death and new blood vessel formation.

All of these theories remain unproven and there is still much to be learnt about how the human body works. Regardless of the mechanism, we can't change our genes anyway, but we can modify our behaviours. So to minimise the risk of getting cancer, stop smoking, eat lots of fruit and vegetables, reduce red meat intake, keep fit and stay lean.

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