Atherosclerosis in Ancient Mummies Revisited

Many of you are already aware of the recent study that examined atherosclerosis in 137 ancient mummies from four different cultures (1).  Investigators used computed tomography (CT; a form of X-ray) to examine artery calcification in mummies from ancient Egypt, Peru, Puebloans, and arctic Unangan hunter-gatherers.  Artery calcification is the accumulation of calcium in the vessel wall, and it is a marker of severe atherosclerosis.  Where there is calcification, the artery wall is thickened and extensively damaged.  Not surprisingly, this is a risk factor for heart attack.  Pockets of calcification are typical as people age.

I'm not going to re-hash the paper in detail because that has been done elsewhere.  However, I do want to make a few key points about the study and its interpretation.  First, all groups had atherosclerosis to a similar degree, and it increased with advancing age.  This suggests that atherosclerosis may be part of the human condition, and not a modern disease.  Although it's interesting to have this confirmed in ancient mummies, we already knew this from cardiac autopsy data in a variety of non-industrial cultures (2, 3, 4, 5).

The more important point is that atherosclerosis does not equal heart attack.  Atherosclerosis is an important risk factor, but extensive cardiac autopsy studies have suggested that traditional cultures with near-zero heart attack incidence have coronary atherosclerosis (6, 7, 8, 9).  Although they tend to have less atherosclerosis than industrial populations when adjusted for age, differences in atherosclerosis alone cannot explain their remarkable resistance to heart attacks: other factors must be involved.  These could include the tendency of the blood to clot, the tendency of atherosclerotic plaque to rupture, and perhaps the diameter of the coronary vessels.  

Some have used the mummy paper to argue the view that it's silly to try to eat like our ancestors because they got sick just like we do.  The paper does not support this view, for two reasons.  First, as I said previously, atherosclerosis is not the only risk factor for heart attacks, and we have extensive cardiac autopsy data from multiple non-industrial cultures indicating that the actual rate of heart attacks was very low, even when adjusted for age (10, 11).  And second, although arterial calcification was common in all cultures represented by the mummies, it was less common in the coronary arteries, where it matters most for heart attack risk.  

The paper reported that only 4 percent of ancient mummies showed coronary calcification, with a mean age at death of 36 years (77 male, 44 female).  However, this figure is misleading because it includes mummies in which the heart was absent and no measurement could be made.  If we use the number of mummies that included hearts as the denominator*, the percentage jumps to 15 percent of mummies with coronary calcification.  Two of the 6 mummies with coronary calcification were Unangan arctic hunter-gatherers (2 of the 6 Unangans examined).  These people had an extreme diet and lifestyle by necessity, and it's possible that something about their lifestyle was bad for the coronaries (low plant food intake, constant smoke inhalation?), though the sample size was too small to draw statistical inferences about the Unangan population as a whole.  If we remove Unangans from the analysis, only 10 percent of the mummies exhibited coronary atherosclerosis.

If we want to compare these data with modern populations, we have to compare specifically with studies that examined calcification.  We can't compare with studies that looked at less severe forms of atherosclerosis by autopsy or other imaging techniques (e.g. fatty streaks), because these are much more prevalent than calcification.  Most studies that specifically examined calcification indicate that calcification of the coronary arteries is roughly twice as prevalent in modern populations as it was in the ancient mummies  when comparing people of a similar age (12, 13, 14), though some have found a similar prevalence (15).

This is consistent with autopsy data from contemporary and historical non-industrial populations, which indicates that they do have coronary atherosclerosis, but usually to a significantly lesser extent than modern industrial populations (16, 17, 18).  The mummy data do not overturn our thinking about atherosclerosis; they simply confirm what we already knew from other sources: developing atherosclerosis with age is part of being human, but the modern diet and lifestyle increase its severity, particularly in the coronary arteries, contributing to a higher risk of heart attack.

* For this calculation, I used intact hearts = 1 and heart "remnants" = 0.5 to get an estimated denominator.