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The greatest health problem of the Middle Ages? The Four Horsemen revisited

If you ask someone to name a health problem of the Middle Ages, most people would name the Black Death bubonic plague (Yersinia pestis) epidemic; it is certainly the most famous of all medieval health problems. But was it really the biggest health challenge medieval people faced? To put it another way, if the World Health Organisation gave you a time machine and told you to solve one health problem, which would you choose?

One way to answer this is to calculate the 'burden of disease'. This uses a methodology developed by the World Health Organisation to estimate how much a specific health problem affects people’s lives. You start by estimating how many people have the condition, what age they get it at, how long it lasts and how severely it affects their life. If it kills them, you total up how many people it kills and how many years it kills them before the age you would expect them to die at; from this, you can total up how many total years the condition takes away from human life. Then, for non-lethal cases, you total up how many years people live with the condition as a disability and how much it disables them. The result is 'Disease Adjusted Life Years', which is how many years of human life and life quality the disease costs the population.

Applying this methodology to ancient populations is a challenge; even with modern populations experts end up estimating a lot of parameters. We used a combination of data on diseases among developing nations, historic data from post-medieval Britain such as seventeenth century London Bills of Mortality, and skeletal data to estimate what health conditions people people had and how they affected them.

The results are surprising. The biggest health problem of the Middle Ages was everyday infectious diseases – things such as gastrointestinal infections, measles, smallpox, whooping cough, typhoid, and scarlet fever. While we can’t distinguish most of these skeletally and historically, they took the biggest toll on human populations by far. The most deadly single identifiable disease was tuberculosis. Bubonic plague was perhaps 10th or 12th in the list. Yes, the Black Death killed half the population of England in one year (1348-9) – but it wasn’t present in England at all before then, and after that it only recurred once a decade or so and it had a much lower mortality rate (5-10%) when it did. War and famine, however much they frightened medieval people and were catastrophic when they happened, weren’t statistically big killers.

A graph showing disability adjusted life years

Chart: J. Robb

Or, to put it another way, if you were going to update the medieval Four Horsemen of the Apocalypse based on statistical data, they would be Death, Infectious Disease, Infectious Disease and Infectious Disease.

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