The importance of ABO blood types in transfusions is unquestioned. And the associations between blood type and certain diseases are pretty convincing. But some “scientists” have linked blood type to some pretty wacky stuff.

In the first part of the 20th century it seems that there was nothing some researchers didn’t think was connected to blood type. Type A people were said to have the worst hangovers.  People with type B blood were supposed to defecate more than other types.  Some thought type Os had the best teeth.  Among military personnel, people with type O supposedly had weaker characters and type Bs were more impulsive.

Even in more modern times the less-than solid science surrounding blood types continues.  Case in point: Eat Right 4 Your Type.  This diet advice book suggests that certain ailments are caused by negative reactions between blood cells and sugar-binding proteins found in food.  The book recommends specific foods for each blood type to counteract these effects.  Critics argue, however, that there is no evidence supporting these ideas (although they admit the diet advice itself is not too bad.)

In Japan, asking “What’s your blood type?” is like asking someone “What’s your sign?” Popular books, magazines and TV programs discuss how blood type contributes to a person’s personality. Write-ups of celebrities, video game characters and even political candidates include blood type so as to help people form their impressions. Matchmaking services and employers even use blood type to help determine compatibility with mates and job assignments.

People with type A blood are supposed to be sensitive perfectionists who can veer towards anxiousness. Type Bs are happy folks who can have eccentric and selfish streaks.  Type O people are said to be curious and generous on the positive side, but also sometimes stubborn. People with type AB are thought to be artsy and mysterious, ideas that probably reflect the rareness of this blood type.

The problem is, just as there’s no plausible link between the motions of the stars and a person’s fate, the idea that blood type is linked to a person’s personality, dietary needs or dental fitness is pure fantasy.  Our blood types may be different, but there’s no reason to think that explains all of our differences.

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Not long after Karl Landsteiner first described the different ABO blood types, scientists started looking for associations between blood type and other human traits.  Some of their theories were truly weird (more on these tomorrow!), but some have held up to scientific scrutiny.

Venous Thromboembolism (VTE)
People with non-type O blood (A, B and AB) have been shown to be at increased risk for VTE.  The reason is thought to be that these people have higher levels of the clot-inducing proteins factor VIII and von Willebrand factor in their blood.  Having non-type O blood further raises the already increased risk for VTE in people who carry the Factor V Leiden and prothrombin G20210A mutations.

Cancer
Since the 1950s, scientists have found that people with type O blood have decreased risk for stomach cancer compared to people with type A.  Other cancers (pancreatic, breast, ovarian, cervical) also occur at lower rates in people with type O blood.  No one is quite sure why this is.  It could be that the sugars found on type A blood cells, which are also expressed by other cells in the body, might somehow help cancers grow more aggressively.  Alternatively, some research has shown that regardless of person’s own blood type, tumors express the type A sugars. In people with type A blood, these sugars go unnoticed by the immune system because they are considered normal.  But in people with type O blood, these new sugars are recognized as foreign, spurring the immune system to destroy the tumors.

Stomach Ulcers
Although stomach cancer is less prevalent in people with type O blood, stomach ulcers are more common in people with this blood type.  The sugars that define the different blood types are also found on cells in the gastrointestinal tract.  Research has shown that these sugars influence the ability of H. pylori, a type of bacteria responsible for a large number of stomach ulcers, to attach to the lining of the stomach.  People with type A or B blood (and hence A or B sugars on their stomach cells) have fewer H. pylori receptors than people with type O.

Severe Malaria
In people infected with malaria, more severe disease is seen in those whose red blood cells are induced to form rosettes, large aggregates that block small blood vessels.  Studies have shown that people with type O blood form fewer, smaller and more easily broken up rosettes than people with type A, B or AB blood.  This is probably because the sugars found on the non-O blood cells end up helping to create larger clumps of cells.

Infectious Disease
Some studies have shown that certain bacterial and viral infections are more or less likely in certain blood types.  For example, type A blood has been linked to a predisposition to “glue ear,” which is caused by infection with Pseudomonas aeruginosa. And some studies suggest that people with type O or B blood are less susceptible to smallpox. The research supporting these and other claims of an impact of blood type on infectious diseases are not as strong as the other associations listed above, however.

(23andMe customers can get a prediction of their ABO blood type based on their DNA data through the new ABO Lab feature.)

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When it comes to blood transfusions, what’s good for one person might be deadly for another.

This might seem obvious today, but until 1900 the idea of “blood types” wasn’t understood. A person in need of a transfusion could find himself getting a donation from just about anyone, and sometimes even an animal!

But in 1900 Austrian scientist Karl Landsteiner noticed that when the blood of different people was mixed together the cells would often clump up, a process he correctly attributed to an immune reaction between the two blood samples. By the next year he had used this clumping reaction to define three main types of blood, which he named A, B and O. (The fourth blood type, AB, was identified in 1902 by two other scientists, Decastello and Struli.)

After hundreds of years of performing blood transfusions unguided, scientists finally had what they needed to safely transfer blood between people. In 1907, the first blood transfusion utilizing the new typing techniques was successfully carried out, and by World War I transfusions were being performed safely on a large scale.

But knowing what blood to give someone and having it on hand are two different things.

Blood banks are faced with the daunting task of making sure there is enough blood of the right type for everyone who needs it at all times. Blood type O, the “universal donor,” tends to be overused. This presents a problem for the approximately 40% of Americans are type O and thus can receive only this type in a transfusion. If supplies run low, their lives could be in danger. At the same time, donated blood with the rare B and AB types can sit unused for so long that it becomes outdated and must be discarded.

One solution to managing the blood supply would be to transform all blood into type O, thus making it suitable for everyone. In the early 1980’s scientists found a way to do this using an enzyme from coffee beans that could strip certain sugars off of type B blood cells. Clinical trials showed that this method was safe and effective, but the method itself was too time consuming and costly to ever be of clinical use. New research, however, has identified bacterial enzymes that can carry out this same process more efficiently. Research with this new method is still in progress.

(23andMe customers can get a prediction of their ABO blood type based on their DNA data through the new ABO Lab feature.)

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23andMe customers who are curious about the genetic basis of their ABO blood type, or don’t already know which one they have, can now find out using our newest Labs feature.

The ABO blood group is just one of more than 25 that go into giving a person their particular “type,” but it is probably the most familiar. The consequences of a mismatch during a transfusion also make it one of the most critical to know: receiving blood with the wrong ABO type causes a person’s immune system to attack the donated cells, which can lead to uncontrolled blood clotting, shock, acute kidney failure and even death.  Fortunately, these types of mix-ups rarely happen.

The different versions of the ABO gene that give people their type A, B, AB or O blood arise from SNPs that are included on the custom v2 version of the 23andMe SNP chip.  We’re now able to use this information to give customers a prediction of their blood type in our ABO lab, our third offering in 23andMe Labs.  Like other labs, the new ABO offering has its own community so customers can compare notes, ask questions and share ideas.

In honor of this latest addition, the Spittoon will be taking a look at the some of the science surrounding ABO blood types over the next week. Stay tuned!

(To whet your appetite, check out the SNPwatch posted just yesterday about the relationship between blood type and the risk for pancreatic cancer.)

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A new genetic study has added more evidence to a decades-old association between blood type and the risk for pancreatic cancer.

Close to 42,500 men and women are expected to be diagnosed with pancreatic cancer in the United States this year.  Because there is no effective screening test for the disease and it is often not detected until it has spread, the five-year survival rate for people with pancreatic cancer is only about 5%. The new results, published online this week in the journal Nature Genetics, represent one of the first associations of a common genetic variant with this deadly disease.

Researchers from Harvard and the National Cancer Institute studied more than 4,300 people with pancreatic cancer and 4,500 controls.  They found that each copy of the C version of rs505922 is associated with 1.2 times increased odds of pancreatic cancer compared to two Ts at this SNP.  The study subjects were mainly of European descent, but this association was essentially the same when the small number of people from other ethnic groups (mainly Asian and African American) was also included in the analysis.

(23andMe customers can check their data for rs505922 using the Browse Raw Data feature.)

The non-risk T version of rs505922 is linked to the variation in the ABO gene that results in type O blood.  People with two Ts are type O.  The riskier C version of the SNP is found in people with type A, B and AB blood.

Epidemiological studies from the 1950s and 1960s, as well as more recent reports, have suggested that people with type O blood are at lower risk for pancreatic cancer compared to those with type A or type B blood.  Finding the association of rs505922 with the disease in a genetic study adds more credence to these previous results. What’s still not understood, however, is why people with type O blood are less likely to get pancreatic cancer.

In their concluding remarks, the authors of the study stressed the need for further research into the genetic risk factors for cancer of the pancreas.

“As there are few known risk factors, improved diagnostics and a finer understanding of the molecular pathogenesis are urgently needed…. The discovery of additional genetic risk variants for this highly lethal cancer could contribute to improvements in … prevention, early detection and therapeutic approaches to pancreatic cancer,” the authors write.

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