In Utero Air Pollution Exposure Tied to Poorer Cognition Later in Life

Erik Greb

February 18, 2021

In utero exposure to air pollution is tied to poorer cognition later in life, new research suggests. 

Results of a large, longitudinal study show exposure to air pollution in early life had a small but detectable link to worse cognition between the ages of 11 and 70 years. However, the effect size was small and the results did not support a cumulative effect.

"The life course paradigm is essential in understanding cognitive decline and this is the first study to examine life course air pollution exposure in relation to cognitive health," the researchers, led by Tom C. Russ, PhD, director of the Alzheimer Scotland Dementia Research Centre, Edinburgh, UK, write.

The findings were published online January 8 in Journal of Alzheimer's Disease.

An Important "First Step"

The researchers note there has been a consistent link between air pollution and cognitive decline and dementia. However, it is unclear whether this increased risk occurs via long-term exposure or whether there are critical periods in life where exposure is particularly harmful.

"A key barrier to clarifying this relationship is the dearth of historical air pollution data," the investigators note.

To investigate the potential link between air pollution and cognitive change over more than 60 years, the researchers analyzed data from 572 participants in the Lothian Birth Cohort 1936 with information on lifetime residential history. 

Participants took the Moray House Test of cognitive ability at age 11 years and again at age 70, 76 and 79 years. Covariates included sex, IQ at age 11 years, social class, and smoking.

The researchers used the EMEP4UK atmospheric chemistry transport model to estimate ambient concentrations of fine particulate matter with a diameter of 2.5 µm or less for the years 1935, 1950, 1970, 1980, and 1990.

They combined these estimates with contemporary data from the year 2000 onward to estimate participants' lifetime exposure to air pollution. The researchers also calculated emissions of nitrogen oxides, sulfur oxides, ammonia, nonmethane volatile organic compounds, and carbon monoxide for the years of interest.

The investigators found a small association between exposure to higher levels of air pollution in 1935, when participants were in utero, and a worse cognitive trajectory from age 11 years to age 70 years (β = –0.006, P = .03).

There was no support for other critical/sensitive periods of exposure or an accumulation of risk (all P > .05).

The investigators acknowledge that due to the various methodologies used to produce the wide range of emissions estimates, the study results have large degrees of uncertainties.

Nevertheless, they note the findings represent "the first step in a new area, and we look forward to a greater understanding of the life course effects of air pollution on the brain in coming years."

Insidious Threat?

Dr Kaarin Anstey

Commenting on the study for Medscape Medical News, Kaarin J. Anstey, PhD, professor of psychology and director of the University of New South Wales Ageing Futures Institute, Kensington, Australia, said the findings raise questions about the insidious nature of air pollution and its effects on early brain development.

"One wonders whether there are critical periods of childhood development when pollution exposure is more detrimental to long-term health and whether there are measurable neuronal differences between infants exposed to air pollution and those who are not," said Anstey, who was not involved with the study.

The study's strengths, she said, include the availability of cognitive data in childhood and old age of study participants; the availability of air pollution data at various time points that were linked to residential history; and adjustment for important measures of socioeconomic status such as parental education.

Its weaknesses include the self-reported and retrospective character of the residential history data; the long interval between cognitive testing at ages 11 years and 70 years; and the incomplete data on cumulative exposure and exposure to other pollutants, said Anstey.

"Improvements in wide-scale environmental monitoring will hopefully provide better time sampling of exposures and allow for estimates of cumulative exposure to pollutants," she added.

Improving the analysis of complex datasets to include multiple time points, Big Data techniques will help provide better models of exposure patterns, she said.  

Anstey noted that the long duration of the adult life course also allows for exposures to other potentially confounding risk factors — and that the latter may not be captured during research assessments.

"One approach to compressing the time needed to study the life course is through accelerated longitudinal cohort studies," said Anstey. "These [studies] involve commencing cohorts in different years with overlapping assessments."

The research also raises the question of how to accurately account for health inequities in environmental health research, given that babies exposed to air pollution also are more likely to be socially disadvantaged.

"The research also raises the question of whether air pollution exposure in utero impacts other organs and increases the long-term risk of heart and respiratory diseases," said Anstey.

The study received funding from the United Kingdom's Natural Environment Research Council, the Chief Scientist Office, and the Medical Research Council. Russ and Anstey have disclosed no relevant financial relationships.

J Alzheimers Dis. Published online January 8, 2021. Full text

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