Atherosclerosis: The Human Condition?

 I've written about mummy abuse before, but today the press is having a field day with the preliminary findings of the Horus study, an examination of atherosclerosis in ancient mummies. Luckily, you don't have to listen to them, because the study is available online for anyone to read. It's also pretty readable as studies go.

The Horus study took a sample of mummies from around the world and CT scanned them for evidence of atherosclerosis, which is accumulation of fatty materials on artery walls. 

Here are the raw numbers: 

137 total mummies, 34% (47 total) with evidence of atherosclerosis (25 definite, 22 possible)

  • 20% in aorta
  • 18% in iliofermoral
  • 18% in popliteal or tibial
  • 12% in carotids
  • 4% in coronary arteries

76 Ancient Egyptians (farmers), 38% (29) with evidence of atherosclerosis

51 Peruvians (farmers), 25% (13) with evidence of atherosclerosis

5 Puebloeans (forager-farmers), 40% (2) with evidence of atherosclerosis

5 Unanagan (true hunter-gatherers living in the Arctic), 60%(3) with evidence of atherosclerosis

Obviously, with such disparate sample size, differences were not statistically significant. Detailed tables give information about each mummy, which is very helpful.

The "with evidence" is important because we are dealing with mummies here and interpreting calcifications are atherosclerosis. Even modern CT scanning of living humans is not perfect at identifying atherosclerosis. 

What is really interesting is that these people had very different lifestyles: the Peruvians probably ate a high-carbohydrate diet with lean meats, whereas the Unanagans lived in polar regions and ate mostly marine animals. 

I think this can put to rest the idea that Ancient Egyptian mummies had plaque because of their high socioeconomic status allowing them to eat a high-fat diet. But it also questions the idea that a high omega-3 diet can prevent it.

There are a great many factors though that can contribute to atherosclerosis though and the fact that it exists in these different populations emphasizes that we shouldn't forget them. There are several infections that can contribute, smoking and exposure to smoke from primitive cooking fires is also a factor the researchers mention. In the end this is not a study about diets, as most press accounts would have you believe. I have to say that the best coverage comes from the Washington Post, and the worst I've seen is at NPR (inapprorpriately makes it about modern diets) and the Atlantic (fails to mention non-dietary factors).

As I've read different arctic mummy studies over the years, I've made this very incomplete spreadsheet that gives a little idea as to how many different conditions some of these people suffered from. The ones from the Zimmerman papers are from the same cave as the arctic mummies in this study. Live was certainly no picnic. Despite the fact that they are hunter-gatherers, it is pretty debatable whether or not the harsh arctic lifestyle is one ancestral to humans, which is why it is important to gather data from savanna and jungle foraging cultures, who probably live lifestyles closer to what humans did for most of our history as a species. Looking at the mummy data, it seems pretty evident that the arctic lifestyle is one that humans live tenuously, unable to keep their body temperature up without smoky fires and possibly suffering from a fair amount of vitamin deficiencies and famine.

But let's not forget that the atherosclerosis levels are still lower than modern levels. In a study of modern humans, by age 50 atherosclerosis was present in 82% of men and 68% of women, whereas in the mummies at an estimated age of 40-49 years (n=43) only around 55% of mummies evidenced the condition and in the mummies older than fifty (n=20) it was closer to 40% (and interestingly little evidence of sex differences). Even more alarming, a study in the US of those aged 14-19 showed that ALL had atherosclerosis of the aorta (compared to 20% of mummies), and 50% had atherosclerosis of the coronary arteries*, whereas only 4% of mummies showed evidence of this, all of these mummies estimated to be in their 40s and 50s. This study is not an exoneration of modern diets and lifestyles.

Of course the data is of vastly different quality, but if you are going to try to use this study to show that humans have always been unhealthy, this is the reality of the comparison.

And that atherosclerosis is a complex condition that does not always lead to disease. In studies of forager-horticulturalists like the Kitavans (who smoke like chimneys, though cigarettes are probably less unhealthy that arctic cooking fires, which produce coal-miner-like lungs) it has simply been assumed they did not have high rates of atherosclerosis because they did not have high levels of diseases associated with the condition, but in reality this might not be the case because atherosclerosis does not always lead to these diseases. As Chris Masterjohn has written, the connection between atherosclerosis and disease requires the plaque to rupture. There are many factors at play here, from the composition of the plaque to where it is located. 

But if anything, this study shows the need to not assume atherosclerosis is low just because disease is low. Since there are few relevant studies even on different Western dieters, it's hard to say if there exists a diet that can possibly prevent this condition. 

* Though as Stephan Guyenet points out, the stats in the paper are marred by the fact that they are counting mummies without hearts in the denominator, without them the number rises a bit, but still not to modern levels