The evolution may explain why humans are prone to heart attacks, according to a study

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(CNN) – A third of the world's deaths are due to cardiovascular disease caused by atherosclerosis, when the arteries are clogged by adipose deposits. Although it is common for human beings to have heart attacks, the same event is rare in mammals. Now, researchers believe they understand why.

Risk factors for cardiovascular disease in humans can include age, hypertension, obesity, smoking, blood cholesterol, and inactivity. However, in 15% of cardiovascular events caused by atherosclerosis, none of these risk factors are on hand.

The closely related mammals, such as captive chimpanzees, share some of the same risk factors for cardiovascular disease: high blood pressure, inactivity, and high blood lipids.

But these chimpanzees rarely have heart attacks. If they do, it is not due to atherosclerosis; the cause is the healing of the heart muscle, which remains to be explained.

Researchers believe that human ancestors lost a single gene, the CMAH, 2 to 3 million years ago, resulting in a higher risk of cardiovascular disease. This gene included a molecule of sialic acid sugar called Neu5Gc. Monkeys and chimpanzees have kept this gene and molecule over time.

In a new study, the mice were modified to exhibit a similar deficiency in this molecule, which resulted in a double increase in atherosclerosis compared to unmodified mice. The study was published Monday in the journal Proceedings of the National Academy of Science.

"The increased risk seems to be motivated by many factors, including hyperactive white blood cells and a tendency to diabetes in human-type mice," said Dr. Ajit Varki, Distinguished Study Author, Distinguished Professor of Medicine and cellular and molecular medicine at the University of California School of Medicine in San Diego. "This may help explain why even vegetarian humans without any obvious cardiovascular risk factors are still very prone to heart attacks and strokes, while other evolutionary parents are not."

Even though humans do not own this gene and the Neu5Gc molecule, those who regularly eat red meat are exposed to it. By consuming it as a by-product of red meat, the human body reacts with an immune response and chronic inflammation.

The modified study mice were fed a diet similar to that of humans who consume red meat: high in fat and rich in Neu5Gc. This led the mice to develop an additional 2.4 fold increase in atherosclerosis.

"The loss of ADCM during human evolution probably contributes to a predisposition to atherosclerosis by intrinsic and extrinsic factors. [dietary] factors and future studies might consider using this more humane model, "wrote the authors of the study.