Could your blood type determine your risk of major cancers, infertility and stomach ulcers, as well as diseases such as cholera and malaria?
For years, the idea that blood groups had any medical significance beyond blood transfusions was dismissed by scientists.
It hasn’t been helped by the celebrity’s favourite, the ‘blood group diet’, which claims your blood type determines how your body responds to certain food.
But a growing number of studies is revealing how our blood groups may make us more prone to lethal illnesses — or even protect us from them.
The latest research into blood types shows that having group O blood can lower your risk of heart attacks.
Researchers at Pennsylvania University discovered this benefit in a study involving 20,000 people. Their research, to be published in The Lancet, found that most people who have a gene called Adamts7 face a significantly raised risk of suffering a heart attack. But in people with blood group O who have the Adamts7, there is no raised risk.
Dr Muredach Reilly, the lead researcher, says this knowledge may help to develop new therapies for people at risk of heart attacks. Such drugs may mimic the beneficial effect of the O blood group gene.
Only 40 per cent of people in Britain know what their group is, according to the National Blood Service. But in future, we may be far more keen to learn it — and to understand its life-saving implications.
Our blood group is determined by genes inherited from our parents.
Millennia of evolution have split human blood into four types: 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 are AB.
What distinguishes each type are their antigens (the immune defence systems) on the surface of the red blood cells. Each blood group type evolved to provide defences against lethal diseases.
But each has its own weaknesses, too. People with type O blood are at less risk of dying from malaria than people with other blood groups. But they are more vulnerable to cholera and stomach ulcers caused by viruses and bacteria.
For a long time, the study of blood groups and disease was discredited — thanks to the Nazis.
Otto Reche, a Nazi German ‘professor of racial science’, claimed in the Thirties that pure Aryans all had blood type A.
The main ‘enemy’ blood group was, he said, B type. He used this to identify ‘inferior’ races for persecution during Hitler’s rise to power.
While such claims are scientifically absurd, in Japan there is still widespread discrimination on the grounds of blood group. In the Twenties, Japanese scientists claimed blood groups produced different personalities.
The idea became so ingrained that in World War II, the Imperial Army formed battle groups based on blood type.
The idea resurfaced in the Seventies and a rash of Japanese best-sellers has spread the belief that type As are sensitive but anxious; Type Bs are cheerful but focused; Os are outgoing but stubborn; and ABs are arty and unpredictable.
This theory has a dark side. Bura-hara (blood-group harassment) is common in Japan. Company chiefs often consider candidates’ blood types when picking staff.
Children at some kindergartens are also divided by blood type. Matchmaking agencies provide blood-type compatibility tests.
Nevertheless, there is serious science behind the idea that blood groups can hold the secret to fighting deadly diseases.
In the Fifties, research at four London hospitals found the risk of developing gastric cancer was much higher for people with blood group A than for those with blood group O. But people with group O had a greater risk of peptic ulcers.
This month, those findings have been confirmed by investigators at Sweden’s Karolinska Institute, which studied more than a million people over a period of 35 years.
The lead researcher, Dr Gustaf Edgren, says people with group A may be more susceptible to gastric cancer risks such as smoking, alcohol and use of non-steroidal anti-inflammatory drugs.
Type O people may be more vulnerable to a bacterium that can cause peptic ulcers, Helicobacter pylori.
Last October, U.S. scientists showed that a woman’s blood group can affect her chances of becoming pregnant.
The study of more than 560 women undertaking fertility treatment found that those with blood type O were up to twice as likely to have a lower egg count and poorer egg quality, which could affect the chances of conceiving.
Women with blood group A seemed to be better protected against their egg counts falling over time.
Researcher Edward Nejat, from New York’s Albert Einstein College, says the exact reasons for a link between blood group and ovarian reserve was not clear.
Blood groups have been linked to other reproductive troubles. Last month, a study at Harvard University found that women with AB or B group blood have a raised risk of developing ovarian cancer.
There are also fears that AB blood may double or even treble the risk of pregnant mothers suffering from the potentially lethal blood pressure condition pre-eclampsia.
This finding could be harnessed to identify women at higher risk.
Other research has found that people with type AB and B blood have a much higher risk of developing pancreatic cancer.
Meanwhile, people with type O might be less at risk of cancer, but research shows they are also more vulnerable than others to norovirus, the potentially lethal vomiting and diarrhoea bug.
And men with type O might be more prone to piling on the pounds, say Danish researchers.
They have found that type O males who are exposed routinely to pollution at work have a significantly raised risk of obesity compared with men of other blood types.
The researchers, at Copenhagen’s Bispebjerg University Hospital, speculate that the pollution sets off chronic inflammatory responses in the men’s bodies that can result in them becoming overweight.
It’s a good excuse anyway.
Taken overall, such a weight of medical evidence might prompt us to question why we are not told of the health threats we might face due to our blood type. But in the UK, there is little work in this field.
Professor Mike Murphy, of the NHS Blood and Transplant authority, says: ‘Our colleagues in the U.S. have become increasingly involved in this type of research, particularly in trying to harness the power of blood types to fight infectious diseases. But the interest in Britain is sparse.’
Indeed, Britain’s highest-profile proponent of blood-type therapy is not a scientist at all; it is Cheryl Cole.
The X Factor judge is a fan of the ‘blood group diet’, which is based on the idea that different blood types process foods differently.
To lose weight, people with group A are told to follow a vegetarian diet, while group O should eat meat and shun dairy and wheat.
‘It has made such a difference to how I feel and my energy levels,’ Cole has gushed in a Hello! magazine interview.
‘Before, I was like “energy schmenergy” and didn’t believe it. But now I believe it 100 per cent.’
Her enthusiasm is not shared, however, by the British Dietetic Association.
A spokesman says: ‘Cutting out food groups is never a good idea. This diet could lead to significant deficiencies such as calcium.’
Meanwhile, a lone group of British researchers is trying to turn blood-group science into a bona-fide lifesaver in one area: malaria.
The effort is being led by Alex Rowe, an infection specialist at Edinburgh University’s School of Biological Sciences.
Her work shows that people with blood group O are resistant to the tropical disease, which kills millions every year.