If you need to receive a blood transfusion, it’s vital to find out your blood type. Otherwise, you could end up with a severe reaction. However, your blood type might influence so much more, including your health. How is this the case? Can you do anything to influence the outcomes?

Did you know that each year 4.5 million lives are saved by blood transfusions? According to the American Red Cross, this equates to someone needing a blood transfusion every two seconds. Close to 21 million blood components are transfused each year in the US. However, many people don’t know their blood type.

Blood is grouped by two main factors. The ABO blood group system was discovered in 1901 by the Austrian scientist Karl Landsteiner. The system uses antigens (a protein on red blood cells) to classify type. Based on the type of antigen, your blood will be categorized as Type A, Type B, Type AB, or Type O. The other aspect taken into consideration is a different antigen, the Rhesus, or Rh, factor. You either have the factor (Rh+), or you don’t (Rh-). There are eight common blood types (A+, A-, B+, B-, AB+, AB-, O+, or O-). Check out the Blood Type Percentages Table to see how common each type is.

While ABO and Rh are the most common antigens, there are more than 600 others. The presence or absence of them creates “rare blood types.” Your blood type is considered rare if you lack antigens that 99% of people are positive for. If you somehow lack an antigen that 99.99% are positive for, your blood type is extremely rare. Certain blood types are unique to specific ethnic or racial groups.

How is Blood Type Determined?

Your blood type is passed down to you from your parents. Both the ABO and Rh antigens are genetically determined. There are a lot of combinations that can be made. Take a look at the Blood Type Determination Table to see all the possible ones for ABO grouping. When it comes to the Rh factor, if a baby receives an Rh-positive allele (gene) from each parent, they’ll be Rh-positive. If the baby gets a negative Rh allele from each parent, they’ll be Rh-negative. If the parent has one positive and one negative Rh allele (making them Rh-positive), they could pass either one down to your child.

If you’re wondering what your blood type is, there are ways to find out. The first is to ask your healthcare provider to order a blood type test. The second option is to donate blood because they’ll do a blood type test as part of the process and let you know the results. The third possibility is to purchase an at-home blood typing test.

Blood Donation

The reason it’s vital to know your blood type, especially when receiving a blood transfusion, is because when antigens come into contact with substances unfamiliar to your body, such as a blood type that doesn’t match yours, it triggers a response from your immune system. The reaction can be severe, even fatal. This is why no hospital will transfuse blood to patients without first doing tests to determine their blood type. To find out which blood types are compatible with others, see the Blood Type Donation Table.

What happens if it’s an emergency with no time for a blood type test? You’ll receive O- blood because it’s compatible with all other blood types. For this reason, people with O- blood are referred to as “universal donors.”

The Rh factor is usually only a concern during pregnancy. If the mother’s and baby’s Rh status don’t match, the mother’s immune system may react as if it’s allergic to the baby. Thankfully, there are injections pregnant women can have to avoid this reaction.

Blood Type and Medical Conditions

There has been increasing research on how your blood type can affect your health in the past few decades. While further study is needed to confirm the findings, the data shows that your blood type may put you at risk for specific medical conditions.

A 2015 study in BMC Medicine found that a gene present in people with A, B, or AB blood types indicates a 15% increased risk for a heart attack, especially if the individuals live in an area with high pollution levels. This is because non-O blood types have 25 to 30 percent higher levels of blood-clotting proteins. A different report from the journal Blood Transfusion discovered that individuals with A/B blood types are more likely to suffer from venous thromboembolism (a blood clot in a vein) than O types.

Research from 2014 published in the journal Neurology indicates that people with AB are 82% more likely than people with other blood types to develop cognitive issues that could lead to dementia. One possible reason for this is that this blood type can lead to high blood pressure, high cholesterol, and diabetes. According to an analysis published in the journal Diabetologia, people with a blood type of A or B have up to 21% greater risk of developing type 2 diabetes than those with type O. These conditions can cause cognitive impairment and dementia.

The ABO gene may play a role in heightened cancer risk. It’s been connected to several kinds of cancers, including lung, breast, colorectal, prostate, liver, stomach, and cervical cancers. Unfortunately, there’s no definitive explanation as to why this is the case.

An evaluation of data published in the journal Human Reproduction notes that type O may interfere with pregnancy. Women with this blood type were twice as likely to have high levels of follicle-stimulating hormone (FSH), which indicates fewer egg cells for fertilization. Another study published in the Journal of Assisted Reproduction and Genetics observed that women with O or A blood types were less likely to experience successful IVF (in vitro fertilization) than those with type B.

A new study from the Karolinska Institute in Sweden looked at Swedish health registries with more than five million people for links between ABO blood type or Rh-positive or Rh-negative blood groups and more than 1,000 diseases. They found 49 diseases linked to ABO blood types, and one connected to the Rh group. Their conclusions confirmed that people with type A blood are more likely to experience a blood clot and that those with type O blood are more likely to have a bleeding disorder. Also, they confirmed that women with type O blood, especially if they were Rh-positive, are more likely to experience pregnancy-induced hypertension. Furthermore, they found a new connection between having type B blood and a lower risk of developing kidney stones.

When it comes to COVID-19, the jury is still out on whether blood type plays a role in the likelihood of contracting the virus. A 2020 study from researchers at Harvard Medical School found that blood type doesn’t affect who becomes sick with the coronavirus. However, more recent studies from Chinese researchers show that people with type A blood may be more susceptible.

Another study involving a review of medical records of 7,770 people who tested positive for the virus found that those with type O blood had a lower risk of contracting the virus. While type A blood was more likely to acquire it, they were less likely to need a ventilator. Unfortunately, those with type AB blood were more likely to not only catch the virus but also need to use a ventilator. As of right now, scientists concur that there isn’t a strong enough connection between a person’s blood type and COVID-19 to consider blood type as a risk factor for contracting the virus.

Blood Type and Personality

Besides medical conditions, blood type has been thought to be linked to personality. This is a Japanese concept called ketsueki-gata. In 1930, Japanese professor Tokeji Furukawa published a report in The Journal of Social Psychology called “A Study of Temperament and Blood-Groups.” He argued that blood types A, B, O, and AB each have a unique effect on personality.

According to Furukawa’s principles, type A is linked with creativity, cleverness, cooperativeness, stubbornness, and uptightness. Type B is supposed to be strong, passionate, empathetic, decisive, selfish, and erratic. Type AB is known for rationality, adaptability, indecision, criticalness, and forgetfulness. Type O is confident, determined, resilient, intuitive, self-centered, and unstable.

From 1984 to 1985, over 200 publications printed papers on blood type personality, resulting in the enduring popularity of the concept. The belief remains widespread in Japan and other Asian nations. It is also increasingly garnering interest in Western countries, such as the United States. In fact, a whole industry of customized products for different blood groups is available. When it comes to dating, someone might reject a potential partner based on fears of incompatibility due to blood type. It’s even been linked to discrimination in the workplace.

Since Furukawa’s research relied heavily on questionnaires and didn’t provide any empirical evidence, it’s been heavily criticized. Yet, studies about ketsueki-gata have continued well into the 21st century all over the world. One Japanese study published in PLOS ONE found that some personality traits differed between blood groups. However, even the researchers noted that there wasn’t enough data to prove the connection. Essentially, no rigorous scientific study has been able to establish a link between blood type and temperament.

Blood Type and Diet and Exercise

Another topic surrounding blood type that has become popular is diet. Naturopath Peter J. D’Adamo created the Blood Type Diet in 1996. He claims that the foods you eat react chemically with your blood type. So, by following a diet designed for your blood type, your body will digest food more efficiently. The results are weight loss, more energy, and disease prevention.

Per the plan, type O people should have a high-protein diet heavy on lean meat, poultry, fish, and vegetables, while light on grains, beans, and dairy. Type A individuals should eat a meat-free diet based on fruits and vegetables, beans and legumes, and whole grains. Type B folks should avoid chicken, corn, wheat, buckwheat, lentils, tomatoes, peanuts, and sesame seeds. Instead, they should eat green vegetables, eggs, certain meats, and low-fat dairy. Type AB persons should focus on tofu, seafood, dairy, and green vegetables while avoiding caffeine, alcohol, and smoked or cured meats.

The Blood Type Diet also recommends exercises based on your blood type. For type O, the best workouts are high-intensity, like interval training, running, and plyometrics. For type A, the best activities are Pilates, yoga, tai chi, and isometric exercises. For type B, the best workouts are group cardio workouts that are slightly lower impact and resistance training. For type AB, the best workouts include walking, hiking, or other low-impact exercises. They should also consider yoga and tai chi.

Unfortunately, there’s no scientific evidence that eating for your blood type makes you any healthier. All four ways of eating are primarily based on natural, healthy foods, which is a considerable step up from the standard diet of processed junk food. So, if you go on one of these diets and your health improves, it’s probably related to better eating and not your blood type. Many experts point out that The Blood Type Diet doesn’t address medical conditions, such as diabetes, heart disease, high blood pressure, or cholesterol.

While it’s helpful to know your blood type, remember that it’s just one factor contributing to your risk for certain health conditions. Also, keep in mind that most research linking blood type and health conditions looks at population studies, which means that it can only find an association between these two things, not conclusively prove that blood type is the cause of a specific condition.