There’s no single “best” blood type, but Type O (especially O negative) comes closest to earning that title. It offers the most versatility in emergencies, carries a lower risk of heart disease and blood clots, and provides some protection against severe malaria and possibly COVID-19 infection. That said, every blood type has tradeoffs. Type O comes with a higher risk of stomach ulcers, and Type AB has unique advantages of its own.
The answer depends on what you’re optimizing for. Here’s how each blood type stacks up across the dimensions that matter most to your health.
Why Type O Stands Out in Emergencies
Type O negative blood is the universal donor type, meaning it can be transfused to anyone regardless of their blood type. Only about 7% of people have it, but it’s the first thing doctors reach for when a trauma patient is bleeding heavily and there’s no time to check their blood type. That makes O negative donors extraordinarily valuable to blood banks, and it means O negative individuals can donate to virtually anyone.
O positive blood, which about 36% of people carry, is almost as versatile. It can go to any Rh-positive recipient, which covers roughly 77% of the population. If you’re the one receiving blood, though, Type O is slightly less flexible. You can only receive O blood, while people with Type AB positive can receive blood from any type, making them the “universal recipients.”
Type AB Has Its Own Advantage
While Type O wins for red blood cell donation, Type AB is the universal plasma donor. Plasma from AB donors can be given to patients of any blood type because it lacks the antibodies that would attack recipients’ red blood cells. AB positive is the rarest common blood type, found in only about 2% of donors, so AB plasma is always in demand. If you’re AB positive, you may not be able to donate red blood cells to as many people, but your plasma is uniquely valuable.
Heart Disease and Blood Clot Risk
This is where Type O has its clearest health advantage. A study of 1.5 million blood donors published in the American Heart Association’s journal Circulation found that people with non-O blood types (A, B, or AB) had significantly higher rates of dangerous blood clots. Compared to Type O, non-O individuals were about 80% more likely to develop deep vein thrombosis or pulmonary embolism. The risk was even more pronounced for pregnancy-related blood clots, where non-O types faced more than double the risk.
The heart attack and stroke numbers were smaller but still meaningful: a 10% higher risk of heart attack and a 7% higher risk of stroke for non-O types. These are population-level statistics, so your personal risk depends heavily on lifestyle, diet, and other genetic factors. But blood type contributes a baseline level of risk that you can’t change, and Type O gets the better end of that deal.
The underlying reason involves clotting proteins. People with Type A, B, or AB blood tend to have higher levels of a key clotting factor that circulates in the bloodstream. This makes their blood slightly more prone to forming clots, particularly in veins.
Malaria Protection
In regions where malaria is common, Type O blood provides a striking survival advantage. Research published in the Proceedings of the National Academy of Sciences found that Type O was associated with a 66% reduction in the odds of developing severe malaria compared to non-O blood types.
The mechanism is well understood. The malaria parasite causes infected red blood cells to clump together with uninfected ones in sticky clusters called “rosettes,” which block small blood vessels and cause organ damage. The A and B sugar molecules on red blood cell surfaces act as docking points for this clumping. Type O cells lack these molecules, so while rosettes can still form, they tend to be smaller and fall apart more easily. This is likely one reason Type O is the most common blood type globally: in areas with historically high malaria rates, carrying Type O gave people a better chance of surviving to pass on their genes.
COVID-19 and Infection Risk
Early in the pandemic, researchers investigated whether blood type influenced COVID-19 outcomes. A large multi-institution study led by Harvard Medical School researchers found no connection between blood type and disease severity once someone was already infected. Blood type didn’t predict who needed intubation, who died, or who developed severe inflammation.
There was, however, a notable finding about susceptibility. Symptomatic people with Type O blood were less likely to test positive for COVID-19 in the first place, while those with Types B and AB who were Rh positive were more likely to test positive. So Type O may offer some protection against initial infection, even if it doesn’t change outcomes once you’re sick.
Where Type O Falls Short
Type O isn’t universally advantageous. There is a well-documented link between Type O blood and a higher risk of peptic ulcers, the painful sores that develop in the stomach lining or upper intestine. The bacterium H. pylori, which causes most ulcers, appears to colonize the stomach more aggressively in Type O individuals. Researchers believe this happens because the same sugar molecules that are absent from Type O red blood cells also affect the stomach lining, changing how the bacteria attach and how wounds heal. In Type O individuals, the process of ulcer repair may be impaired, leading to more bleeding and more persistent sores.
Cancer Risk Varies by Type
Blood type also plays a role in certain cancer risks, though the effects are modest. People with Type A blood have roughly 1.34 times the risk of developing stomach cancer compared to other blood types. The reasons aren’t fully understood, but they likely involve how the immune system interacts with the sugar molecules on cell surfaces that define your blood type. These molecules don’t just sit on red blood cells. They appear throughout your digestive tract and other tissues, where they can influence inflammation and cell behavior.
Cognitive Health and Type AB
Type AB may carry a disadvantage when it comes to brain health. A study published in Frontiers in Neurology found that men with the AB genotype had a 34% higher risk of Alzheimer’s disease compared to other blood types. The risk was even more pronounced in men who also carried a specific genetic variant (APOE e4) associated with Alzheimer’s, where AB blood type was linked to a 75% increase in risk. These findings were specific to men and to certain genetic backgrounds, so they don’t apply equally to everyone with AB blood.
Pregnancy and Rh Factor
Beyond the ABO system, the Rh factor (positive or negative) matters most during pregnancy. If you’re Rh negative and your baby is Rh positive, your immune system can develop antibodies that attack the baby’s red blood cells. This condition, called Rh disease, used to be a serious threat but is now rare thanks to a preventive injection given around 28 weeks of pregnancy and again within 72 hours of delivery. The treatment is highly effective at preventing your body from making these antibodies in the first place.
About 14% of donors are O negative and roughly 23% of the population overall is Rh negative, so this is a real consideration for a substantial number of pregnancies. The key is early screening. If your provider knows your Rh status, the problem is almost entirely preventable.
How Common Each Blood Type Is
Your blood type is determined by genetics and varies widely across populations. Based on donor data from the UK:
- O positive: 36%
- A positive: 28%
- O negative: 14%
- A negative: 8%
- B positive: 8%
- B negative: 3%
- AB positive: 2%
- AB negative: 1%
These numbers shift by ethnicity and region. Type B is more common in South Asian and East Asian populations, while Type O dominates in Central and South America. Type A is most prevalent in parts of Europe and Scandinavia. Whatever your blood type, the biggest factors in your long-term health remain the ones you can control: how you eat, how much you move, and whether you manage conditions like high blood pressure and cholesterol. Blood type adds a small nudge in one direction or another, but it rarely overrides everything else.