Epidemiology and human health causation

Epidemiology is a combination of the Greek words epi (over = upon), demio (demos = human population), and logy (logos = science). It is the science that focuses on human populations. In the past dozen years or so, the word "epidemiology" became widely known to the public due to the leak of radioactive materials at the Fukushima Daiichi Nuclear Power Plant and the global COVID-19 pandemic. In both cases, society sought evidence to answer the question of what happens in human beings, not in animal experiments. This pursuit shone a spotlight on radiation epidemiology and infectious disease epidemiology, which have a long history of academic research.

The word "evidence" first began to be used in the 1990s in the form of evidence-based medicine (EBM). Since then, the pursuit of evidence has become so common that many people have asked questions such as "what is the evidence for the coronavirus vaccine?" In this article, I would like to look back at some previous examples to show how evidence has been constructed and established through epidemiological research, which is my area of expertise.

Origins of modern epidemiology and infectious diseases

The first time modern epidemiology was recognized by society was during the cholera epidemic in London, England in the 1850s. To summarize briefly, anesthesiologist John Snow recorded cholera patients and deaths in central London on a map, and discovered that many cases were concentrated around the water of specific water companies and specific public wells. Snow confirmed that cholera in the areas subsided when use of the wells was blocked. This was about 30 years before German bacteriologist Robert Koch discovered the cholera bacterium. Even without knowing the pathogen or the mode of infection, a PDCA (Plan, Do, Check, Action) cycle was implemented based on observations of human populations, and the epidemic was resolved.

It is truly a web of causation that the birth of epidemiology, which emerged during the London cholera epidemic, was brought to field hospitals during the Crimean War by Florence Nightingale who cared for cholera patients, and was supplemented by adding statistics, which led to the quelling of infectious diseases among the wounded. Known as an angel in white, Nightingale was also the first female member of the Royal Institute of Statisticians. In order to reduce the number of deaths from infectious diseases, which was actually greater than the number of deaths in battle, Nightingale examined ventilation frequency and bed spacing based on epidemiological observations and data analysis. This established the foundation for evidence of avoiding the "three Cs," which were widely introduced in response to the modern COVID-19 pandemic.

Epidemiology and evidence in Japan

The web of causation also extended to Japan. In 1875, Japanese doctor Kanehiro Takaki studied at the medical school and hospital that housed the Florence Nightingale Faculty of Nursing and Midwifery. Takaki learned Western medicine as well as early epidemiology. After returning to Japan, he worked as a naval surgeon to investigate the cause of beriberi, a disease which was prevalent at that time. As a result of his epidemiological observations, Takaki concluded that the cause of beriberi was diet. He conducted a training voyage across the Pacific Ocean, which was the same as previous voyages except for a change in diet. As a result of the different diet, the crewmembers returned home without a single death from beriberi (with the previous diet, 45% of the crew developed beriberi and about 7% died). Afterwards, beriberi was completely eliminated from the navy. The web of causation continued until 30 years later, when Japanese chemist Umetaro Suzuki discovered vitamin B1 (a deficiency of which causes beriberi) in rice bran, which is removed during rice polishing to create white rice. There is a long history behind the establishment of evidence for beriberi prevention. For example, in the 16^th century Age of Discovery, a logbook by explorer Vasco da Gama records a sailor who suffered from scurvy recovering by eating oranges. Medical books from 17^th century England and 18^th century Japan state that "coffee is effective against dropsy (similar to beriberi) and scurvy." Furthermore, it is known that in the early 15^th century, the Zheng He fleet of the Ming Dynasty in China piled soil on the deck to grow vegetables and drank low-fermentation tea, which enabled them to successfully navigate their long voyages. This demonstrates that evidence can only save lives if it is widely shared (it is said that at least one million people died of beriberi between the 16^th and 18^th centuries). In Japan, even after the navy established the beriberi prevention method, the army continued to search for the beriberi bacteria (Army Surgeon General Rintaro Mori studied basic microscopic medicine in Germany), and there was a tragic history of many more deaths from beriberi than those from bullets, etc., in the subsequent Sino-Japanese War and Russo-Japanese War. Although evidence for beriberi prevention had been scattered around for centuries, this case made it painfully clear that lives can only be saved by obtaining widespread agreement and adoption from politicians and ultimately society.

A distant causal relationship revealed over a period of 100 years

Epidemiology was born from the study of infectious diseases and has contributed to the discovery of nutritional deficiencies. Epidemiology then grew significantly as the prevention of cardiovascular disease. Infectious diseases have an incubation period of several days, while nutritional deficiencies are several months. In contrast, for example, the effects of smoking on cardiovascular disease appear years or even decades later. Identifying distant causal relationships is difficult for only clinicians who treat patients in hospitals. Instead, it has required the persistent efforts of epidemiologists around the world. Major contributions were also made by computers, whose performance improved dramatically in the 20^th century, and the accompanying leaps in statistics. This made it possible to identify in succession the risk factors for cardiovascular disease that we now take for granted, such as smoking, salt, lack of exercise, and unbalanced nutrition, as well as the effects of each factor.

Finally, I would like to introduce one more epidemiological study that identified a distant causal relationship. A researcher noticed a correlation between high infant mortality rates in each region of England in the early 20^th century and high mortality rates from coronary heart disease in the same region from 1968 to 1978. Children who died in infancy are obviously different from those who died from coronary heart disease 50 or 70 years later. However, nutritional epidemiologist David Barker wondered if they shared a common cause: malnutrition. He investigated the possibility that areas with poor nutrition had more infant deaths and more deaths from coronary heart disease. This seemingly outlandish hypothesis was published in 1986 and was called the Barker hypothesis. It was later discovered that records of all births and the outcomes of children from 1911 to 1933 had been kept in Hertfordshire, England. Analysis of these records showed that children with lower birth weights were more likely to die of myocardial infarction in the future. So what is the relationship between low birth weight and nutritional status? Epidemiological data from the tragedies of World War II contributed to elucidating this missing link. From 1944 to 1945, the Netherlands was under Nazi German occupation. People in the Netherlands starved and suffered a winter of famine. There were records of children born during this winter. When the food rations for pregnant women dropped from 1,500 kcal per day to around 700 kcal, the weight of pregnant women dropped by 5 kilograms. Also, the birth weight of babies dropped by 400 grams and birth height dropped by about 4 centimeters. However, these physical characteristics quickly recovered after the liberation of the Netherlands. It was found that children who experienced this winter in the early stages of pregnancy had higher obesity levels at age of 50, higher blood sugar levels at age of 60, and higher mortality rates due to cardiovascular disease. These accumulations led to the establishment of a hypothesis called the DOHaD hypothesis (Developmental Origins of Health and Disease), which contributed to the rise of social epidemiology dealing with health disparities across generations. In Japan, this hypothesis led to the establishment of new standards for weight gain during pregnancy in 2021 (encouraging thin to normal pregnant women to gain more weight than before).

The future of epidemiology

In the age of big data and data science, there are many epidemiological studies around the world that have tracked human populations from fetal stages. Epidemiology, which once identified strong, short-term causal relationships (infectious diseases) and contributed to disease prevention, has now shifted its focus to evaluating weak, complex, distant causal relationships. My own research specialty is using statistical methods to unravel causal relationships. However, rather than focusing on whether something is correct or not, I aim to achieve higher certainty and disseminate information for new research in the future. In the Department of Integrated Science and Engineering for Sustainable Societies of the Faculty of Science and Engineering, which is an organization that values learning in multiple fields, I will sow the seeds of epidemiological learning with the aim of conducting research and developing human resources to unravel causality that transcends generations.

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[Reference Literature]

• Oka, K. The virtue of coffee and vitamins learned from the history of scurvy and dropsy. The Japanese Journal for History of Pharmacy. 2016. 51(1): 5-10.
• Okamura, T. Kakke ronso no hikari to kage Rikugun no kakkesangai ha naze fusegenakattanoka (provisional translation: Light and shadow of the beriberi debate: Why couldn't the army prevent the beriberi disaster?) Azusa Shoin. 2020.
• Edited by the Japan Epidemiological Association. An Introductory Textbook of Epidemiology (Revised 4^th Edition). Nankodo. 2024.
• Matsuda, M., Takaki, K. Kakke wo nakushita otoko (provisional translation: Biography of Kanehiro Takaki: The man who eliminated beriberi.) Kodansha. 1990.
• Barker DJ, Osmond C. Infant mortality, childhood nutrition, and ischemic heart disease in England and Wales. Lancet. 1986; 1: 1077-81.
• Barker DJ, Osmond C, Law CM. The intrauterine and early postnatal origins of cardiovascular disease and chronic bronchitis. J Epidemiol Community Health. 1989; 43: 237-40.
• Buklijas T, Al‑Gailani S. A fetus in the world: Physiology, epidemiology, and the making of fetal origins of adult disease. History and Philosophy of the Life Sciences. 2023. 45: 44.
• Osmond C, Barker DJ, Winter PD, Fall CH, Simmonds SJ. Early growth and death from cardiovascular disease in women. BMJ 1993; 307(6918): 1519-24.
• Syddall HE, Aihie Sayer A, Dennison EM, Martin HJ, Barker DJ, Cooper C. Cohort profile: the Hertfordshire cohort study. Int J Epidemiol 2005; 34(6): 1234-42.

Ayano Takeuchi／Associate Professor, Faculty of Science and Engineering, Chuo University
Areas of Specialization: Epidemiology and Biostatistics

Ayano Takeuchi was born in Kanagawa Prefecture. She graduated from Morimura Gakuen Senior High School. She graduated from the Epidemiology and Biostatistics Laboratory in the Department of Health Sciences and Nursing of the Faculty of Medicine, the University of Tokyo in 2004. After completing her Master’s and Doctoral Programs in the Division of Health Sciences and Nursing of the Graduate School of Medicine, the University of Tokyo, she became an Assistant Professor in the University of Tokyo in 2008. After serving as a researcher at the Center for Environment and Health Research of the National Institute for Environmental Studies in 2012, and a Full-Time Lecturer (School of Medicine) in the Department of Preventive Medicine and Public Health, Keio University in 2014, she assumed her current position in April 2022. She holds a Ph.D. in health science (the University of Tokyo). She serves as a senior epidemiology expert (Japan Epidemiological Association).

Her areas of specialization are epidemiology and biostatistics.

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