Can your blood type protect you from getting dementia?

Blood types are mysterious things — no one knows for sure why we have different groups, for instance.

Yet science is revealing how having a particular blood type can play a crucial hidden role in many aspects of health, from our chances of suffering sex and fertility problems, to whether we develop Alzheimer’s, lethal blood clots or even cancer.

The difference between blood groups is down to a combination of sugars and proteins that coat red blood cells.

Based on this, we can all be classified into one of four main groups: A, B, AB and O. Around 44 per cent of Britons are type O, 42 per cent are type A, 10 per cent type B and 4 per cent AB.

A study published last week suggests that men with type O are four times less likely to experience impotence than men with blood types A, B or AB. According to the research, by Ordu University in Turkey and published in the journal Archives of Italian Urology and Andrology, blood type may be as important a risk factor for impotence as smoking, being overweight, and high blood pressure.

Although the exact reason is unclear, scientists said the penis has one of the highest amounts of veins in the body, and that something in blood type A may damage the lining of these veins, causing erectile dysfunction.

Fewer than half of English adults know their blood type, according to the NHS Blood and Transplant service, and many of us only find it out when we give blood.

Yet knowing our group may help us protect our own health. For although it is not clear why these groups emerged, it is known some blood types offer defence against different diseases.

For example, studies by the University of Toronto in 2014 indicate that people with type O are better protected against severe malaria than other blood types.

This seems to be because human immune cells are better able to recognise infected type-O blood cells than other types, and are more likely to target them.

But immunity seems to be only part of the story. Blood type also affects female fertility, and type A seems to be significantly better than type O. Studies have consistently found that women with type-O blood exhaust their body’s store of eggs earlier in life.

A 2011 Yale University study of more than 560 women in their mid-30s having fertility treatment found those with type O were twice as likely to have a lower egg count and poorer egg quality than those with group A. Researchers said this meant that they were less likely to become pregnant.

Separate research suggests that the hereditary genes which determine type O blood may also be responsible for this premature egg depletion.

There is some good fertility news for women with type O blood, however. Last year an Italian study, in the journal Blood Transfusions, found that they have a lower risk of pre-eclampsia — high blood pressure in pregnancy, which can be dangerous for mother and baby — than women with other blood groups.

Having type-O blood has another advantage in that it appears to reduce people’s risk of degenerative brain diseases such as Alzheimer’s. Following brain scans on 189 Britons, researchers at Sheffield University discovered that those with type-O blood have more grey matter (which processes information) in crucial areas associated with speech, coordination and balance than those with type A and B blood.

‘We think that grey-matter levels are linked with the genetic factors that determine a person’s blood group,’ says Annalena Venneri, a professor of clinical neuropsychology who conducted the 2015 study. ‘These seem to affect how their brain develops.’

She adds that because type-O people develop more grey matter when young, they can afford to lose more of it in old age without developing dementia.

Indeed, a 2014 study of 495 people in the journal Neurology found that people with type O had a lower risk of developing cognitive impairment than those with types A and B. Professor Venneri says education, diet and exercise can also protect against the effects of losing grey matter, so it may be good to concentrate advice about this on people in non-O groups.

‘We could suggest to these people that, as a preventive measure, they should do more stimulating brain activities to counteract their blood-group,’ she told Good Health. ‘A healthy diet and exercise could help, too.’

A similar picture emerges with regards to potentially lethal artery and vein blockages.

In the journal Circulation last year, a five-year study of 1.5 million blood donors in Denmark and Sweden found that those with type O blood had around a 30 per cent lower risk than other blood types of developing clots that cause deep vein thrombosis, thromboembolisms (obstruction of a blood vessel in the body), and pulmonary embolisms (blockage of an artery in the lungs).

Furthermore, research shows that people with type B are far more likely than other blood groups to suffer recurrent thrombo- embolisms, though the reason is not yet understood.

These findings may help to explain why having type-B blood has been linked to an increased risk of premature death.

Type O also seems to have a protective effect against some cancers, such as stomach and liver cancer, studies suggest.

This growing body of compelling evidence might seem to support the fad for ‘blood-type’ diets, where popular books have encouraged people to stick to food regimes that ‘suit’ their group.

Some proponents recommend, for example, that people with type-O blood consume meals high in protein and fat, as their bodies are somehow configured to process these ingredients efficiently.

Not so, conclude nutritionists at Toronto University. In 2014 they studied 1,400 people on blood-type diets. They did find that their general health improved after months on the diets.

But it didn’t matter which blood-type regimen a person was on — or even if it matched their own blood type — the improvements were much the same. This was because the dietary regimens were themselves all quite healthy.

The Canadians declared in the journal PLoS One: ‘Our findings do not support the “Blood-Type” diet hypothesis.’