A study of the arteries of ancient Egyptians has challenged the received wisdom that the illness is simply down to unhealthy modern lifestyles.

In 2008, Greg Thomas, a cardiologist from California, was in Cairo for work. While there, he visited the Egyptian Museum of Antiquities with another cardiologist, Adel Allam of Al Azhar University in Cairo. They came across the mummy of King Merneptah, a pharaoh who lived 3,200 years ago. The description on Merneptah’s case said he had suffered from atherosclerosis, the buildup of plaque on artery walls. Both men were sure this must be wrong. How could an ancient Egyptian have had heart disease, when most of the risk factors for the disease – obesity, unhealthy diet, smoking and lack of exercise – did not then exist? But could they prove it?

Thomas, medical director of the MemorialCare Heart and Vascular Institute in Long Beach, California and Allam discussed how they could find out more about Merneptah’s arteries. They theorised that any arterial plaques might still be visible on a CT scan, a computerised x-ray technology that produces 3D images. Plaques contain calcium, which degrades slowly – a key reason that bones endure for so long.

After months of negotiation with officials, the pair began scanning the museum’s mummies (ironically, Merneptah was excluded, as Egyptian archaeological officials ruled that royal mummies could not be part of the project). What they found surprised them: many showed clear signs of fatty buildup in their arteries. When the results are adjusted for age (pre-modern people had shorter life-spans, so most of the remains are of people who died in their 40s or younger), the rate of atherosclerosis was about the same as it is for people in modern society, around 40%.

Until then, most researchers had believed that atherosclerosis was largely caused by modern lifestyles. The solution had seemed clear: if we moved more, ate more vegetables and fewer doughnuts, and quit smoking, we would significantly reduce the buildup of the plaques that are a key cause of heart disease.

Thomas and Allam’s results call that view into question. “The evidence that’s emerging is remarkable,” says Thomas. “These results challenge our understanding of the fundamental causes of atherosclerosis.” Since that first study, they have expanded their research, measuring plaque levels in ancient arteries all over the globe – from Egypt, Peru, Mongolia, the American southwest and the Aleutian Islands in the northern Pacific Ocean. All 14 of their “paleocardiology” studies so far have shown that atherosclerosis was common among pre-modern people.

“This work points out that we have had this problem for millennia,” says George Martin, a pathologist from the University of Washington. “So diet and lifestyle may not contribute as much as we thought. That’s a new idea.”

Caleb Finch, a biologist from the University of Southern California, who has also worked on the project, agrees. “Researchers have been confident about the causes of atherosclerosis. Our work suggests we should be less confident.” He says the results suggest that the general process of ageing has more to do with atherosclerosis than previously realised.

Finch is one of more than a dozen collaborators involved in what has become known as the Horus study (the name refers to a major ancient Egyptian deity). The group’s members come from all over the world, and include cardiologists, radiologists, molecular biologists, anthropologists, archaeologists and geneticists. Each week, they gather via conference call to discuss new results and future plans. “It’s a dream team of researchers who really like to push boundaries,” says Thomas. “We’re all doing this for the fun of discovery.”

Since 2008, they have scanned more than 130 bodies. They are now in the midst of scanning remains in Mongolia, and, in a few weeks, will begin looking at Egyptian mummies from the Neues Museum in Berlin. Over the past two years, they have also travelled to the Bolivian Amazon, where they are giving CT scans to members of the Tsimane tribe, a group of largely pre-modern hunter gatherers. Thomas and his colleagues want to gauge atherosclerosis levels among this group, whose way of life likely bears a closer resemblance to that of ancient Egyptians and Peruvians than to people in developed countries. “They are contemporary people living an ancient lifestyle,” Thomas says.

The research is not simply academic – it has significant public health implications. Atherosclerosis is a major factor in cardiovascular disease, which is the leading cause of death in the UK and worldwide; about 73,000 Britons die from it every year, and more than twice that many have heart attacks.

As they continue to expand their work, the Horus researchers emphasise that many key questions remain unanswered – including the origin of the mummies’ atherosclerosis. Thomas and Finch suspect that pre-modern heart disease was caused not simply by genes or ageing, but by another risk factor, one that modern societies no longer face: widespread chronic infection. From tests on tissue samples, they know that many mummies typically had one or more chronic infections, including malaria, tuberculosis, worms or other microbes. One teenage Egyptian mummy had four serious parasites – a level of disease that would be astonishing today.

Such infections can significantly increase levels of inflammation in the body – and, in recent years, researchers have increasingly realised that inflammation can damage the cardiovascular system. In fact, inflammation appears to be the same mechanism through which obesity, unhealthy diet, and sedentary living also cause heart problems. On top of this, pre-modern people probably faced another serious trigger for inflammation: smoke from wood fires used for cooking, heating and lighting. So it is possible that ancient Egyptians, Peruvians, and others had the same illness as modern people – inflammation-induced heart disease – but with different root causes.

Beyond that, Thomas and Finch agree that there are likely to be as-yet-undiscovered reasons behind both pre-modern and modern heart disease, which they are working to discover. “I think there’s something that we’re missing, that could really change our understanding of this disease,” says Thomas. “That’s what is so exciting about this. We could really make a difference.”