Air pollution has been linked to the shrinkage of “white” connective tissue in men’s brains

Air pollution may take a much heavier toll on the mental abilities of men than it does on women, according to a study.

Men living in cities with high levels of pollution appear to lose their faculties for logical and verbal reasoning at a faster rate than women. For older men in the most polluted areas the loss could be equivalent to a year of education or a gap of more than 20 per cent in test scores.

Academics argue that the divide could be attributed to structural differences in the brain that leave men more vulnerable to the shrinkage of “white” connective tissue linked to air pollution. This theory has been challenged by independent scientists.

Public health researchers at Yale University in the United States and Peking University in Beijing analysed the performance of 25,485 people in China on maths and language exams conducted in 2010 and 2014. It is understood to be the first study to examine how these scores changed in relation to both day-to-day fluctuations and long-term trends in exposure to air pollution.

It found that young men and women tended to do equally well in the cognitive tests up to the age of 30, but men tended to do notably better than women later in adulthood.

In the most polluted cities, however, the scores of older men dipped dramatically, especially on the language papers. For every extra ten units on the Air Quality Index, which measures three different kinds of pollutant and runs from zero to 500, the average man was found to lose 2.1 per cent more of his cognitive ability than a woman of the same age in the same area. The index in London ranges from single figures to almost 200. The levels in Beijing tend to range between 35 and 250.

TOXIC CONSEQUENCES

Air pollution has been blamed for 40,000 early deaths a year in the UK and more than three million worldwide. The various particles and gases are known to irritate the lungs and exacerbate respiratory diseases. They have also been linked to a wide range of serious illnesses such as cancer and heart disease.

A report from the London School of Economics suggested that it may be responsible for a rise in road accidents, possibly because it reduces visibility or causes itchy eyes and noses.

In the past five years studies have shown that higher ozone levels make farm workers less productive, and that fine soot particles and carbon monoxide appear to harm teenagers’ exam performance.

The research is published as a working paper on the EconStor website. Xi Chen, assistant professor of public health at Yale, who led the study, said that the impact was large enough to be economically significant. “The gender gap in active white matter is a very plausible mechanism through which air pollution may impose a gender-differentiated impact on cognitive performance,” he said. “Our study might be the first step towards explaining this important phenomenon.”

Barbara Maher, of Lancaster University, who worked on research showing that nanoparticles of magnetite from air pollution can find their way into the brain, said that some important questions needed to be answered. “This paper suggests some gender differences in the impacts of air pollution on brain white matter and grey matter, but the measures of air pollution exposure are very broad-brush,” she said.

Gina Rippon, professor of cognitive neuroimaging at Aston University in Birmingham, said that the authors had misinterpreted the science of grey and white matter. “It would be interesting to know what kind of effects air pollution might be having on brain structure or function, but I do not think this paper is going to help that cause,” she said.

One should not mistake test scores for brain function. Often, the comparative test scores tell us more about unequal education than the brain itself.

William Shockley, one of the inventors of the transistor, in later life made the infamous connection between IQ scores and race in the following statement:

"My research leads me inescapably to the opinion that the major cause of the American Negro's intellectual and social deficits is hereditary and racially genetic in origin and, thus, not remediable to a major degree by practical improvements in the environment."