HEALTH IMPACTS OF AIR POLLUTION: Evidence from the heights of British soldiers in the First World War
- 29 Mar 2017
Smoke pollution from factories in late nineteenth Britain had a highly damaging effect on the health of children as indicated by the height reached in adulthood by those born in the 1890s. New research by Professor Timothy Hatton, to be presented at the Economic History Society’s 2017 annual conference, reveals that the average height of children who grew up in the most coal-intensive parts of the country was nearly an inch (2cm) shorter than those in the least coal-intensive locations.
The study analyses the heights of a sample of 2,235 men who enlisted in the British army around the time of the First World War. Their average height was five feet six inches (167.6cm) and their average age on enlistment was 20.3 years.
These soldiers are also recorded as children in the 1901 census of England and Wales, making it possible to observe their household circumstances and the locality where they grew up. Combining information on coal consumption by industry from the 1907 census of industry with the occupational structure of employment from the 1901 population census provides a measure of industrial coal intensity for each of the 635 registration districts – and the opportunity to relate childhood exposure to pollution to later life health outcomes.
The author explains the findings in more detail:
There is growing concern about the effects of atmospheric pollution on health. In 2016, the World Health Organisation reported that 92% of the world’s population lives in places where air pollution exceeds WHO limits. It is calculated that outdoor air pollution accounts for three million deaths per year. And most of these deaths occur in low- and middle-income countries. The dense smog in China’s cities provides a sharp contrast with the relatively clean air of Western cities.
But it was a different story a century ago. Coal-fired industrialisation in Europe spawned factories that belched black smoke, with little government regulation. Black smoke from these emissions was in the order of fifty times higher than today. Partly for this reason, urban centres had much higher mortality rates than rural areas. Indeed, there is evidence that the mortality gradient by industrial emissions was steeper in nineteenth century Britain than it is in China today.
The more modest levels of atmospheric pollution of recent times, as reflected in concentrations of particulate matter and other pollutants, have been linked to premature death and to a variety of illnesses. Children are especially vulnerable as their lungs are still developing and they are prone to repeated infection. But while there is no shortage of stories of the evil effects of the dark satanic mills of the past on the wellbeing of those who lived nearby, the quantitative evidence is thin.
In the nineteenth century, dense smoke from factory chimneys left a signature in the form of an indelible black coating on the walls of cathedrals and town halls. But the effects on health are more difficult to measure. One assessment of the effect of industrial coal combustion on mortality rates in nineteenth century Britain constructs a measure of industrial coal-use based on the occupational composition of different localities. This index is strongly correlated with local death rates, especially among those under five, and it accounts for one third of the urban mortality penalty.
In our recent study, we use a similar approach to estimate the effects of smoke pollution on the health of those that survived. Our outcome measure is the adult heights of children born in the 1890s. Height is an indicator of health conditions during childhood, and it depends both on the level of nutrition and on the disease environment. These in turn are influenced by socioeconomic conditions in the household and in the locality.
We obtain heights for a sample of 2,235 men who enlisted in the British army around the time of the First World War. Their average height is five feet six inches (167.6cm) and their average age on enlistment is 20.3 years. We find these men as children in the 1901 census of England and Wales, so we are able to observe their household circumstances and, most importantly, the locality in which they were growing up.
To measure exposure to atmospheric pollution, we combine information on coal consumption by industry from the 1907 census of industry with the occupational structure of employment from the 1901 population census. This gives us a measure of industrial coal intensity for each of the 635 registration districts of England and Wales.
How does coal intensity relate to adult height? There is a negative relationship between coal intensity and height. But there are many other influences at work, including genetic variation. We use regression analysis to control for household characteristics, including the social class of the head of the household and the number of siblings in the family. We also control for local population density, which has a strong negative effect on height.
In the presence of these controls, we find a significant negative relationship between coal intensity and adult height. This predicts a difference of nearly an inch (2cm) between the least and the most coal intensive locations (10th versus 90th percentiles).
As our measure of air pollution is indirect, it is possible that an effect on health and height could potentially arise though channels other than the atmosphere. So we look for additional evidence. One piece derives from the fact that the winds that carry atmospheric pollution are predominantly south-westerly. We would expect that coal intensity in districts to the southwest would affect height. This is exactly what we find. Coal intensity in districts to the southwest has a significantly negative effect on height while coal intensity in districts to the northwest does not.
It is possible that we are simply picking up heterogeneity among households that were engaged in different industries. If the effect of coal intensity on height is to be interpreted as reflecting atmospheric pollution, then it should not be affected by the occupation of the head of household. We find that the coal intensity of the household head’s occupation has no effect on the adult heights of children. So the effect of local coal intensity is not simply a composition effect but a genuine locality effect.
There was considerable inter-district mobility in nineteenth century Britain, which could obscure the true locality effects. If for some reason, households with smaller children were more likely to migrate into coal intensive districts, then the effect of coal intensity on adult height could simply reflect the selectivity of migration into districts with heavy industry. But we find little evidence of such selectivity. Indeed in-migrants seem to have somewhat healthier children.
To identify the channels through which atmospheric pollution during childhood affected adult height, we turn to the mortality statistics. Respiratory diseases accounted for over 20% of all deaths of those aged under five. Death rates from respiratory causes varied widely between districts and they are strongly correlated with the death rates from all causes. Looking across districts, we find that our measure of coal intensity has a strong positive effect on the respiratory death rate.
If we interpret the respiratory death rate as a proxy for the local disease environment, then we can use this as an indicator of the channel though which atmospheric pollution affected adult height. We find that height is negatively correlated with local child death rates, and especially with the respiratory death rate. Using coal intensity as an instrumental variable, we find evidence that atmospheric pollution affected adult height through the channel of respiratory disease. So the effect that we observe seems to work through the relevant epidemiological mechanism.
In the past century, atmospheric pollution has fallen to a small fraction of its nineteenth century level. Industrial coal use has dramatically declined and clean air acts have become effective. If this improvement was of the same order of magnitude as the difference between the most and least polluted areas in the nineteenth century, then it would have contributed nearly an inch to the long-run increase in average height.
From the birth cohorts of the 1890s to the those of the 1980s, the heights of British men have increased by 2.75 inches (7cm). So the decline in atmospheric pollution may have contributed significantly to improved health over the long run.