Type O is often called the “healthiest” blood type because it carries the lowest risk of heart disease, blood clots, and stroke. But the full picture is more complicated. Every blood type has both advantages and vulnerabilities, and the differences in absolute risk are small enough that your blood type alone won’t determine your health outcomes. What the research does show is a consistent pattern of trade-offs worth understanding.
Why Type O Has a Cardiovascular Edge
The strongest evidence favoring type O comes from cardiovascular research. 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, and AB) had a 10% higher rate of heart attack and a 7% higher rate of stroke compared to type O individuals. For peripheral vascular disease, the increase was about 6%.
The gap widens dramatically when it comes to blood clots. Non-O blood types face a 2- to 3-fold higher risk of venous thromboembolism, which includes deep vein thrombosis and pulmonary embolism. The reason is biological: people with A, B, or AB blood carry sugar molecules on a key clotting protein called von Willebrand factor. These sugar molecules act like a shield, slowing the body’s natural process of breaking down and clearing the protein. The result is higher circulating levels of clotting factors, which makes blood more prone to forming dangerous clots. Type O blood lacks these protective sugar molecules, so clotting proteins get cleared more efficiently.
Cancer Risk Varies by Blood Type
For certain cancers, type O again comes out ahead. A study in the Journal of the National Cancer Institute tracked participants over time and found that compared to type O, the risk of pancreatic cancer was 32% higher for type A, 51% higher for type AB, and 72% higher for type B. Pancreatic cancer is rare overall, so even a 72% relative increase translates to a small absolute number of additional cases. But the pattern is consistent and statistically significant.
Gastric cancer research shows a similar trend, with type A carrying elevated risk. The underlying mechanism likely involves how blood group antigens on the surface of cells in the digestive tract interact with bacteria and inflammation, though the exact pathways are still being mapped.
Type O’s Disadvantages
Type O isn’t universally protective. One notable vulnerability is fertility. A study published in Fertility and Sterility found that women with type O blood were twice as likely to have elevated baseline FSH levels (a hormone marker that rises when ovarian reserve is declining) compared to women with other blood types. Women carrying the A antigen, meaning those with type A or AB blood, were about half as likely to show signs of diminished ovarian reserve. This doesn’t mean type O women can’t conceive, but it suggests the A antigen may play a protective role in egg supply preservation.
Type O also offers a mixed bag with infectious disease. Research from West Africa shows that type O individuals actually get infected with malaria-causing parasites at higher rates. The protection type O provides appears to target disease severity rather than preventing infection itself, reducing the risk of the life-threatening complications that make malaria deadly. Meanwhile, type O has historically been linked to greater susceptibility to cholera.
Type B and Diabetes Risk
Type B blood has drawn attention for its association with type 2 diabetes. A cross-sectional study published in Medicine found that individuals with blood group B had roughly double the odds of developing type 2 diabetes compared to those with non-B blood types. Types A and AB showed no significant association. The biological explanation isn’t fully clear, but it may relate to how blood group antigens influence gut bacteria composition and metabolic signaling.
Type AB and Cognitive Decline
Type AB, the rarest blood type (found in roughly 4 to 7% of most populations), carries a unique risk for brain health. Research published in Frontiers in Neurology found that the AB genotype in men was associated with a 34% increased risk of Alzheimer’s disease. For men who also carried a genetic variant linked to Alzheimer’s susceptibility (the APOE e4 allele), the risk jumped to 75% higher. The combination of AB blood type and genetic predisposition appears to amplify vulnerability in ways that neither factor creates alone.
What the Longevity Data Shows
If type O were dramatically healthier overall, you’d expect to see it overrepresented among people who live past 100. The data is less convincing than you might expect. A survey of 269 centenarians in Tokyo found that type O made up 28.3% of the group, compared to 30.1% in the general population. Type B was actually overrepresented among centenarians at 29.4% versus 21.9% in controls, despite type B’s associations with diabetes and pancreatic cancer risk. Type A was slightly underrepresented. These numbers suggest that blood type alone is a weak predictor of how long you’ll live.
Putting the Risk in Perspective
The relative risk differences between blood types, while real, are modest compared to the impact of lifestyle factors. A 10% increase in heart attack risk from having non-O blood is real, but smoking increases heart attack risk by 200 to 400%. Obesity, physical inactivity, and poor diet each carry far larger effect sizes than anything your ABO type contributes.
Your blood type is fixed at birth and can’t be changed, which limits its practical value as health information. Where it becomes most useful is in combination with other risk factors. If you have type AB blood and a family history of Alzheimer’s, or type B blood and prediabetes, those overlapping risks might warrant earlier screening or more aggressive prevention strategies. On its own, though, no blood type is a health sentence, and no blood type is a free pass.