Know your ABOs: What does your blood type say about your health?

Knowing your blood type could open up a whole world of valuable new information about your personal health profile

Researchers have investigated blood types as a risk factor for conditions ranging from heart disease to dementia and even susceptibility to ill winter vomiting virus.

Could your blood group determine your health? Researchers at the University of Maryland recently reported in the journal, Neurology, that young adults who suffered early strokes were more likely to have blood type A and less likely to have blood type O. Other researchers have investigated blood types as a risk factor for conditions ranging from heart disease to dementia and even susceptibility to ill winter vomiting virus. Yet despite its importance, many Irish people don’t know their blood type as doctors and hospitals do not routinely check it.

Paul McKinney, operations director at the Irish Blood Transfusion Service, says the organisation has run campaigns with the hashtag #MissingType to raise awareness of the importance of knowing your blood group.

“People rarely think about whether their blood type is A, B or O — many of us don’t even know our own blood type,” McKinney says. “It is important to know your blood type not just because it is useful for health reasons but because it is vital to know if you need an operation that requires a blood transfusion.”

McKinney says the best way to find out what type you are is to give blood, as all new donors are issued a donor card with their blood group.

Your blood type is genetically determined based on the type of proteins, called antigens, found in your red blood cells. There are four main types: Type A (containing A antigens) Type B (B antigens); Type AB (A and B antigens) and Type O (neither A nor B antigens). Each blood group can be either RhD positive or RhDnegative, which means there are eight blood groups in total.

The most common blood type in Ireland is O positive (47% of the population). But the Irish Blood Transfusion Service says there are regional variations, with people in the West of Ireland predominantly O group while more people with RhD negative live on the east coast.

Here’s why your blood type might matter to your health:

Strokes and blood clots

A recent study looked at 48 genetic studies focusing on ischaemic strokes (those caused by a blockage of blood flow to the brain) in younger adults and showed blood type can be a ‘modest’ risk factor for a stroke of this type before your 60th birthday.

Steven J Kittner, a professor of neurology at the University of Maryland Medical Centre, and his team analysed data from 17,000 stroke patients and nearly 600,000 healthy controls and found those aged under 60 who had early strokes were more likely to have blood type A and less likely to have blood type O compared to those who had a stroke in their 70s or 80s or those who never had a stroke.

Blood type A participants were at a 16% greater risk of an early stroke than other blood types, while in O blood types the risk of a stroke was 12% lower, they reported in Neurology.

Kittner says the underlying reason is unknown, but “it likely has something to do with blood-clotting factors like platelets and cells that line the blood vessels as well as other circulating proteins, all of which play a role in the development of blood clots” that can lead to a stroke.

In other studies, people with A blood type have been shown to be at a slightly higher risk of developing blood clots in the legs, known as deep vein thrombosis. In Ireland, one in six people will have a stroke at some point in their lives, and the Irish Stroke Association says you need to monitor your blood pressure and live a healthy and active lifestyle to reduce your risk.

Cognitive decline

Significant memory problems and cognitive impairment, risk factors for dementia, might be more common in people with blood type AB than the rest of the population. A study involving more than 1,000 people aged 45 and above, conducted at the University of Vermont, has shown that people with blood type O had the lowest odds of developing cognitive impairment with blood type AB at an 82% higher risk.

In 2015, neurologists at the University of Sheffield discovered why this might be the case. Blood types play a role in the development of the nervous system and may mean a higher risk of developing cognitive decline. The Sheffield researchers found that people with an O blood type have more grey matter in their brain than those with A, B or AB blood types. As we age, our grey matter volume decreases but those with O blood types had smaller losses in temporal and limbic regions of the brain, including the left hippocampus, one of the earliest parts of the brain damaged by Alzheimer’s disease.

The Alzheimer’s Society of Ireland says staying active mentally and physically can make a difference. Physical activity helps improve blood flow to the brain, providing more oxygen and nutrients. Also, keeping your mind engaged by listening to music or doing puzzles helps with attention and concentration.

Heart disease

People with blood groups A, B and AB may be at a higher risk of heart disease with blood type AB, in particular, being as much as 23% more likely to suffer from heart disease than those with blood group O, according to the Harvard authors of a 2012 study, that included more than two decades of data on 62,000 women and 27,000 men. It found that people with type B blood had an 11% higher risk of heart disease compared with type O. Other researchers, including those working on the renowned Framingham Heart Study at Pennsylvania State University, have since reported a possible 12% increased risk for people with non-O compared with O blood types. 

Your blood type is genetically determined based on the type of proteins, called antigens, found in your red blood cells.

Stomach ulcers

Several researchers have reported people with blood group O are “significantly overrepresented” among patients with stomach ulcers (also called gastric or pectic ulcers) compared with the other blood groups.

Stomach ulcers typically occur when layers that protect the stomach lining from acids are damaged through infection with H. pylori bacteria or through taking aspirin or ibuprofen long-term.

There’s little evidence that stress or certain foods make stomach ulcers worse. Experts don’t know why people with O blood type tend to get more stomach ulcers, but it is thought to be linked to having cells that are the preferred targets of the bacteria.

Ulcers are not always painful, and minor symptoms include heartburn and indigestion, but if you experience sudden pain or pass dark sticky stools, you should seek medical advice.

Covid

A 2020 paper published in the New England Journal of Medicine was the first to suggest that blood type might influence your risk of getting Covid-19 with blood type O seemingly at a lower risk than other blood groups and blood group A at a higher risk.

A review published in Seminars in Vascular Surgery last year found eight of the nine most recent Covid blood type studies showed an association between blood type and susceptibility to Covid infection. But any association is tentative and there is no strong proven connection with some papers published showing bias and weak science, says Martin Maley, a senior lecturer in biomedical science at the University of Sunderland.

“The most important factor remains the number of antibodies you carry from inoculations and previous infections, as well as your level of overall health and fitness.”

The most common blood type in Ireland is O positive.

Is there a connection between blood type and personality?

How you think and behave might be down to your blood group. At least that’s a suggestion put forward by Martin Maley, senior lecturer in Biomedical Science at the University of Sunderland, who has conducted research on the links between personality and blood type.

“Blood groups are usually discussed only in a medical setting, but in Japan it is widely believed there is a link between human blood types and personality traits,” Maley says. It is believed that different personality traits and behaviours are associated with each blood group:

• O are thought to be understanding, rational, organised, outgoing, optimistic and energetic
• A are considered punctual, patient, sensitive, loyal, considerate and responsible
• B are passionate, creative, strong, thoughtful, adventurous and curious
• AB are artistic, serious, genius, caring, rational and indecisive

In a recent survey involving some 1,500 people, Maley found no link between self-reported personality traits and blood type, but he is currently planning a follow-up large peer-reviewed study of university students. “It might be that there is no scientific basis at all to the theories,” he says. “But if there is any association it could help to determine who is more prone to stress or negativity.”