A recent study by economists at the University of Massachusetts Amherst has – for the first time – found a link between exposure to air pollution during early childhood with the development of arthritis later in adult life.

Jamie Mullins, assistant professor in the department of resource economics at UMass Amherst, found that those who were exposed to the 1952 Great Smog of London during their first year of life had a 23.4 percentage point higher incidence of arthritis later in life than those not exposed as infants by virtue of their birth dates and/or the locations of their residence in early life. This increase represents a doubling of the arthritis rate among the exposed population. The higher arthritis rates among those exposed to the Smog in the first year of life are clearest for rheumatoid arthritis (RA) – a 14.9 percentage increase – versus osteoarthritis, which saw a 9.5 percentage point increase.

“These findings are important today, as millions of people continue to be exposed to episodes of extreme air pollution each year. In fact, the World Health Organization estimates that 91% of the world’s population lives in areas that experience unhealthy levels of air pollution,” Mullins says.

The report, “Arthritis diagnosis and early-life exposure to air pollution,” was co-authored with Andrew Shepherd, a 2018 UMass Amherst resource economics master’s degree recipient, and was published in the journal Environmental Pollution. The study is one of the first to link early life exposure to air pollution with medical conditions much later in life and the first to do so for arthritis, which is estimated to afflict 54.4 million American adults – nearly 23% of the adult population.

Air pollution is currently implicated in some 7 million deaths per year, but such tallies only take account of deaths from issues related to the respiratory and circulatory systems. According to Mullins, their new results “show that a wider set of physiological systems are harmed by air pollution exposure than is generally considered. This suggests that many more health issues and deaths are likely impacted by air pollution than are currently accounted for.”

The Smog that blanketed London from December 5-9, 1952, was caused by an unexpected temperature inversion, which trapped emissions from the city’s coal-burning heating stoves and diesel-powered buses near ground-level. The resulting ambient pollution mixed with moisture to form a thick, foul-smelling fog that disrupted life in the city and ultimately led to as many as 12,000 deaths in the four months following the event.

The authors interpret their results as causal effects of the Smog, saying that “estimates are identified through the difference in outcomes between groups that are effectively randomly determined by time and place of birth,” and that “any plausible alternative explanation for our results would need to have impacted only London, contemporaneous (or nearly so) to the Smog, and drive higher incidences of arthritis, and especially of RA. We are unable to identify any candidate factors or events that meet these criteria.”

The researchers fear that their results imply that the health effects of poor air quality have likely been dramatically underestimated because such effects continue manifesting for decades after exposure and extend beyond cardiopulmonary issues.

“While the pollution mixture of the Great Smog differs from the pollution mixtures of other places and times, the continued combustion of coal and diesel globally suggests parallels are likely to exist between the Great Smog and today’s worst pollution events,” they conclude. “More work is needed to map the mechanisms through which air pollution taxes health over both the short and long terms in order for the full costs of pollution to be better understood and addressed. We hope that the findings of this article will contribute to more complete assessments of the costs of air pollution and potentially aid medical clinicians and researchers seeking to understand, diagnose, and treat arthritic diseases.”

The complete report, “Arthritis diagnosis and early-life exposure to air pollution,” is available via ScienceDirect.

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