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How blood type is determined -

Like eye color, blood type is passed on genetically from your parents. Blood types are determined by the presence or absence of certain antigens, which can trigger an immune response if they're foreign to the body.

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ABO and the most common blood types -

The ABO blood group system classifies blood types according to the different types of antigens in the red blood cells and antibodies in the plasma. Alongside the RhD antigen status, they determine which blood type will match for a safe transfusion.

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Group A -

The surface of the red blood cells contains A antigen, and the plasma has anti-B antibody. Anti-B antibody attacks blood cells that contain B antigen.

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Group B -

The surface of the red blood cells contains B antigen, and the plasma has anti-A antibody. Anti-A antibody attacks blood cells that contain A antigen.

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Group AB -

The red blood cells have both A and B antigens, but the plasma doesn't contain anti-A or anti-B antibodies. People with type AB can receive any ABO blood type.

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Group O -

The plasma contains both anti-A and anti-B antibodies, but the surface of the red blood cells doesn't contain any A or B antigens. Any ABO blood type can receive this type of blood.

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Rhesus factor -

Some red blood cells have the Rh factor or antigen. If the red blood cells contain the Rh antigen, they're Rh positive. If they don't, then they're Rh negative.

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Testing for blood type -

A blood test can determine an individual’s blood type. In a lab, the blood is mixed with three different substances to see how they react. Each substance will contain A or B antibodies, or Rh factor. Observing these reactions will enable the technician to identify a person’s blood type.

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Heart disease -

Research shows that O blood types have a lower risk of coronary heart disease. Experts aren’t sure why. But some believe it might be because other types are likely to have higher cholesterol and higher amounts of a protein that’s linked to clotting.

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Memory -

A small study showed that people with AB blood type are more likely to develop thinking and memory problems, which can lead to dementia, than people with other blood types.

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Life span -

Chances are higher you’ll live longer if you have type O blood. Experts believe this is mainly due to a lowered risk of disease in heart and blood vessels.

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Stomach cancer -

A, AB, and B blood types are more at risk than type Os, especially people with type A blood. Experts think this might be because of H. pylori, an infection more common with type A blood. It's usually found in the stomach, causing inflammation and ulcers.

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Stress -

Stress increases the body's level of cortisol, also known as the stress hormone. People with type A blood tend to have more cortisol, which can make it harder for them to deal with stress.

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Pancreatic cancer -

The risk is higher if you're types A, AB, or B. Molecules in types A and B red blood cells help the H. pylori bacteria grow in your gut. This can make you more likely to get pancreatic cancer.

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Malaria -

You can get malaria when an infected mosquito bites you. Luckily, if you have blood type O, it's harder for the parasite to attach to the cells.

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Ulcers -

Peptic ulcers are painful open sores that crop up in the lining of your stomach or upper intestine. They seem to occur more often with blood type O. 

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Diabetes -

Type 2 diabetes seems to happen more often in people with blood types A and B. However, more research is needed to understand why.

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Fertility -

In one study, women with low numbers of healthy eggs were more likely to have type O blood than any other type. However, more research needs to be done to understand why.

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Rheumatic disease -

Rheumatic disease is a group of more than 200 conditions that cause pain in your joints, connective tissue, tendons, and cartilage. A 2017 study in Turkey showed that some conditions were more common with blood types A and O. 

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Blood clots -

Venous thromboembolism (VTE) is when your blood clots in a deep vein. Research shows that people with types A, B, or AB blood are at a higher risk of VTE.

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Stroke -

You're at greater risk for a stroke if you have blood type AB. Medical professionals think that’s because it’s more likely to clot than other types.

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Lupus -

Lupus is an autoimmune disease that causes inflammation and pain throughout the body. Studies have found those with blood types A and B had more severe symptoms than other blood types.

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Multiple sclerosis (MS) -

MS is a condition when your immune system attacks a protective layer around your nerves called myelin. It's a lifelong condition that can cause serious disability. Research has found that those with blood types A and B have an elevated risk for developing MS.

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Inflammatory bowel disease (IBD) -

There are two main types of IBD: ulcerative colitis, and Crohn’s disease. Studies both in Italy and South Korea showed that those with blood type O had a lower chance of developing Crohn’s disease.

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Hemorrhage -

Losing a large quantity of blood is common after severe trauma, such as after a car accident or other injury. Blood type O has been noted to suffer more from hemorrhage-related deaths. But more research needs to be done to understand why.

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Risks in pregnancy -

The Rh antigen comes into play during pregnancy, if the mother has Rh-negative blood and her fetus’ blood is Rh-positive. Antibodies from an Rh-negative mother may enter the blood stream of her unborn Rh-positive infant, damaging the red blood cells.

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The bottom line -

Researchers still don’t understand how blood type and certain diseases are related. It’s thought that genetics and environmental factors both play a role in the development of many conditions. But more research is needed to fully understand this link.

Sources: (Medical News Today) (WebMD) (Healthline)

See more: New COVID strain threatens Europe, the US, and beyond

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