How air pollution impacts on the brain’s white matter

Researchers from the Barcelona Institute for Global Health (ISGlobal) have found that exposure to air pollution in early life can have lasting effects on the brain’s white matter.

White matter makes up most of the brain’s deepest parts of the brain and is the tissue through which messages pass between different areas of grey matter within the central nervous system. While there is evidence associating air pollution exposure with brain development, the teams felt that research on white matter microstructure in children was limited. 

The research involved a 4,108 strong birth cohort from Rotterdam, with residential air pollution exposure to 14 air pollutants during pregnancy and childhood estimated with regression models. For 1,314 children, the researchers were able to use data from two brain scans – one performed around 10 years of age and another around 14 years of age – to examine changes in the brain’s white matter. 

ISGlobal researcher Mònica Guxens said: ‘Following participants throughout childhood and including two neuroimaging assessments for each child would shed new light on whether the effects of air pollution on white matter persist, attenuate, or worsen.’

The investigation was based around examining levels of  fractional anisotropy… ‘which measures how water molecules diffuse within the brain. In more mature brains, water flows more in one direction than in all directions, which gives higher values for this marker.’

They  found that exposure to PM2.5 and nitrogen oxides was associated with differences in the development of white matter in the brain. Specifically, higher exposure to PM2.5 during pregnancy, and higher exposure to PM2.5, PM10, PM2.5-10, and NOx during childhood were associated with lower levels of fractional anisotropy. This association continued through adolescence, suggesting that air pollution was having a long-term impact on brain development. Every increase in exposure level to air pollution corresponded to more than a 5-month delay in the development of fractional anisotropy.

Michelle Kusters, ISGlobal researcher and first author of the study said: ‘We think that the lower fractional anisotropy is likely the result of changes in myelin, the protective sheath that forms around the nerves, rather than in the structure or packaging of the nerve fibres.’

The researchers point out that these children were exposed to levels of PM2.5 and PM10 concentrations below the current EU recommendations (but above those of the World Health Organization), leading Guxens to conclude: ‘Our study provides support to the need for more stringent European guidelines on air pollution, which are expected to be approved soon by the European Parliament.’