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Why Causality Matters, or the Difference between Scurvy and Beriberi

David Sundahl, 5/4/2016


A teacher of mine, K. Codell Carter, a philosopher and historian of medicine has captured the importance of what he calls the "aetiological stance"--the orientation of medicine toward understanding the causes of disease.

In his book The Rise of Causal Concepts of Disease: Case Histories he points out that medical science up to the 19th century made relatively few advances and little progress. However, once physicians and researches focused on the mechanisms that caused disease, medical science’s “discoveries and powers”--to steal a phrase from Francis Bacon about the proper object of science--skyrocketed. Everything from the virtual end of leechcraft to the effective treatment of many other ailments occurred within the brief period of the late 19th and early 20th centuries and has continued at breakneck speed since. Carter’s careful examination of the progress of medical science shows repeatedly that the attempt by researchers to isolate causes of illness was the key to moving beyond much of what we now think of as superstition.

Carter briefly notes the difference in the scientific progress of curing scurvy vs. beriberi as an example of the power of causality. Scurvy, caused by a deficiency in vitamin C, was described by the famed father of medicine Hippocrates, but not understood causally until 1927. Throughout the two millennia that preceded a true understanding of the cause of scurvy many remedies were prescribed, almost all of them close to the true cause of scurvy. Even as early as the 1830s something like clinical guidelines were developed for the prevention and treatment of the disorder--fresh meat and citrus generally contain enough vitamin C to cure scurvy.

However, lacking a deep understanding of the mechanism for scurvy led to confusion among physicians and researchers. For example, the storage and transport of citrus juices in copper or their exposure to air and sunlight degrade vitamin C content to sub-therapeutic levels. Researchers and practitioners got what we might refer to as “noisy” data. Sometimes lime juice cured scurvy and sometimes not. To make matters worse, the advent of steam ships got sailors from port to port faster, where they could consume good sources of vitamin C. So sailors who might have suffered scurvy decades earlier appeared to be treated successfully with inadequate sources of vitamin C. Without a drive to understand the causal mechanism for scurvy, these guidelines did not evolve much. Researchers were satisfied with knowing that (most of the time) lime juice cured scurvy.

Beriberi, an insufficiency of vitamin B1, had a different trajectory. Although known in the 17th century, the serious study of beriberi did not arise until the 1880s, when researchers were looking not just for guidelines to treat the disorder, but its underlying cause. Immediately, diet was identified as a causal factor for beriberi. In fact, by 1884, a Japanese researcher had determined that beriberi was only found among sailors whose diet consisted almost entirely of rice. One can imagine researchers being satisfied with knowing this and ensuring that sailors had a more diverse diet, as their counterparts had been satisfied knowing that usually meat or citrus cured scurvy. However, where scurvy researchers stopped due to pretty good empirical work, the "aetiological stance"'--the drive to understand causation--kept scientific progress on beriberi moving forward. By the 1890s researchers had settled definitively that a dietary deficiency connected to unpolished rice caused beriberi. And by 1913 researchers knew that a particular extract of rice bran was the deficiency that caused beriberi.

It's not just that causality enables 100% effective treatment, but the drive to understand causes--leads to faster progress. In a world, where big data and its analysis are gaining influence, we cannot forget that there is no substitute for understanding the causation at work in the world around us.