While IT’S handed down from our parents and we all have one, how does your blood type affect your health?

In reality there are more than 300 blood types but they all fall into one of four key groups — type A, B, AB or O, collectively known as ABO.

We each come under one of these groups and, while type O is considered the most common, your blood group is determined by your genetics.

Your parents each pass down their blood type genes and the mix determines your type — so, a type O mum and a type B dad could have a type O or B child, whereas a type O mum and dad could only have a type O child.

What makes the four types different from each other is a molecule — known as an antigen — that attaches to the outside of your red blood cells.

“If you imagine a red cell as a doughnut, think of these molecules as the sprinkles and trimmings on the doughnut,”, according to Professor Robert Flower, from the Australian Red Cross Blood Service.

These antigens are also the reason why blood type might play a role in your health.

They’re not all shaped the same way, they contain different sugars and they can alter how the blood behaves.

This is what impacts your risk of some diseases.

1. Blood type and pancreatic cancer

If you are blood type A, AB, or B, then your chance of developing pancreatic cancer is significantly higher. Molecules in type A and B red blood cells help certain bacteria called H. pylori grow in your gut. It can make you more likely to get pancreatic cancer.

2. Blood type and heart attack & erectile dysfunction

According to researchers from the University Medical Center Groningen in the Netherlands, people with types A, B or AB are nine per cent more likely to have heart attacks than those with type O.

One reason for this, according to Dr Ellen Maxwell from Melbourne Pathology, could be the way the antigens influence a substance called von Willebrand factor, which causes our blood to clot.

“Levels of this are 20-30 per cent lower in people with type O, meaning their blood is simply less sticky compared to non-O individuals,” Ellen explains.

Sticky blood is also thought to be why risk of stroke is higher in A, B or AB types.

Men with these blood types are also more likely to experience erectile dysfunction because the thicker blood may not reach the genitals as effectively as thinner blood.

The antigens might also have an impact on the diseases you’re most at risk of, or how severe they are if you get them.

3. Blood type and strep infection

Malaria, for example, is less harmful for people with type O blood.

“The malaria parasite makes a kind of glue that sticks to the type A antigen, causing cells to clump and leading to severe illness,” Robert said.

“Type O blood doesn’t form these clumps, so infected people don’t get so ill.”

Malaria isn’t the only infection that’s been linked to your blood type.

Recent research at the University of Wollongong School of Biological Sciences in Australia found that group A streptococcal infection, which can lead to everything from a mild sore throat to a serious blood infection, is more likely to attach to type O blood cells.

“The sugars found on O cells are put together in a different way to those found on A and B cells, and we think this makes it easier for the bacteria to hold onto the cells,” according to Dr Martina Sanderson-Smith, from the Illawarra Health and Medical Research Institute, who worked on the trial.

What to eat for each blood type

The Blood Type Diet originally comes from the 1996 book Eat Right 4 Your Type, by naturopathic physician Dr. Peter D’Adamo, and has been kicking around various health forums for nearly three decades.

The general thrust of the diet is that there are optimal foods for people with various blood types O, A, B and AB. Part of the claim hinges on the idea that blood types serve as maps of our ancestral history and genetics, and that the foods commonly eaten by our ancestors are better suited for our bodies, even in the modern day.

Below is a snapshot of the four main blood types and what D’Adamo posits is the best type of diet for each.

Type A: The agrarian or cultivator. According to D’Adamo, those with type A blood should avoid meat — specifically red meat — and eat a plant-based diet rich in fresh fruits, vegetables, legumes and whole grains. Because of more “sensitive immune systems,” they should also avoid processed foods and opt for organic foods whenever possible.

Type B: People with blood type B are dubbed “nomads” by D’Adamo. Folks with type B are encouraged to eat plants but also most meats (except chicken). The diet also cautions against eating corn, wheat, tomatoes, peanuts and certain seeds.

Type AB: People with type AB blood, or “enigmas” as D’Adamo calls them, are a mix between types A and B. The Blood Type Diet encourages these people to eat seafood, tofu, dairy, beans, greens and grains but to avoid corn, beef and chicken. D’Adamo contends type ABs also have lower levels of stomach acid and thus should avoid caffeine and alcohol.

Type O: Also known as the “hunter,” D’Adamo purports that people with this blood type should eat a high protein diet rich in red meat, fish, poultry and some fruits and vegetables. This precursor to the paleo diet cautions type Os against eating grains, legumes and dairy products.