People whose blood type is A, B or AB have an increased risk of heart disease and shorter life spans than people who have type O blood, according to a new study.

But that doesn't mean people with blood types other than O should be overly concerned, because heart disease risk and life span are influenced by multiple factors, including exercise and overall health, experts said.

In the study, researchers followed about 50,000 middle-age and elderly people in northeastern Iran for an average of seven years. They found that people with non-O blood types were 9 percent more likely to die during the study for any health-related reason, and 15 percent more likely to die from cardiovascular disease, compared with people with blood type O. [Beyond Vegetables and Exercise: 5 Surprising Ways to Be Heart Healthy]

"It was very interesting to me to find out that people with certain blood groups — non-O blood groups — have a higher risk of dying of certain diseases," said the study's lead investigator, Dr. Arash Etemadi, an epidemiologist at the U.S. National Institutes of Health.

The researchers also examined whether people's blood type may be linked with their risk of gastric cancer, which has a relatively high incidence rate among the people living in northeastern Iran. They found that people with non-O blood types had a 55 percent increased risk of gastric cancer compared with people with type O blood, according to the study, published online today (Jan. 14) in the journal BMC Medicine.

The association between blood type and people's disease risk and life span held even when the researchers accounted for other factors, including age, sex, smoking, socioeconomic status and ethnicity.

Previous studies have shown that people with non-O blood types may be at higher risk of certain cancers and cardiovascular disease, but it was less clear whether blood type is linked with life span, Etemadi told Live Science.

About 11,000 people in the study provided information about their blood's biochemistry, including their cholesterol levels, glucose levels and blood pressure. But only certain metrics stood out — for example, the people with type A blood tended to have higher levels of total cholesterol and LDL cholesterol, also known as the "bad" cholesterol.

It's possible that higher cholesterol levels could partly explain the increased mortality risk. People with non-O blood types also have an increased tendency to form blood clots, and this higher coagulation might lead to more heart problems, Etemadi said.

Moreover, the gene that is responsible for blood type is on the same chromosome as some of the genes responsible for controlling blood cholesterol, Etemadi said.

But it's unlikely that the cholesterol link is solely responsible for the difference in people's life span, he said. "We think that it's a mixture of both causes that contribute to this increased mortality," Etemadi said.

Although people with non-O blood types may have these increased risks, they should "absolutely not" be concerned that their blood type is the determining factor in their health, said Dr. Massimo Franchini, director of hematology and transfusion medicine at the Carlo Poma Hospital in Italy, who was not involved with the study.

"Belonging to a non-O blood type represents only a risk factor (among many others), and actually, there are many and many millions of people worldwide with non-O blood type that do not have, and will never develop, any of these diseases," said Franchini, who wrote a commentary on the study that was also published in the journal. "Thus, in my opinion, a healthy lifestyle still remains the main factor able to influence the health status of an individual."

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