New Delhi, Aug 24: For Delhiites, the health cost of breathing polluted air may go beyond coughing, breathlessness and heart problems, with a Delhi University review suggesting that prolonged exposure to fine particulate matter (PM2.5) could also affect the brain.
Studies reviewed by DU professors have linked long-term exposure to particulate matter with changes in brain structure, memory, attention and other cognitive functions.
Researchers said PM2.5 can trigger inflammation and oxidative stress, affect the energy-producing system of brain cells and interfere with the blood-brain barrier, which normally protects the brain from harmful substances.
Some of the smallest particles may also reach the central nervous system through the nose and the olfactory pathway, the review said.
The review, conducted by DU professors from the Department of Environmental Studies, examined 129 peer-reviewed articles on the neurological effects of particulate matter and found growing evidence linking long-term exposure to PM2.5 with cognitive impairment and structural and functional changes in the brain.
“Air pollution is no longer only a lung and heart problem; it is increasingly a brain-health problem. Research now links long-term particulate-matter exposure with cognitive decline, impaired neurodevelopment and biological processes associated with Alzheimer’s and Parkinson’s diseases,” Vandana Mishra, one of the researchers associated with the study, said.
Mishra added that fine particulate matter has even been seen to breach the blood-brain barrier, a dangerous side effect of pollution.
One key concern highlighted in the review is that prolonged exposure to air pollution has been associated with changes in the physical structure of the brain.
“A growing body of evidence strongly demonstrates that chronic exposure to ambient air pollution, particularly PM, leads to region-specific structural and functional alterations in the human brain, spanning across developmental and ageing stages,” the study says.
Neuroimaging and other studies have reported reductions in brain volume and cortical thickness, particularly in areas such as the frontal and temporal lobes that are involved in cognition.
These structural changes have been associated with problems in memory, attention and executive functions such as planning and decision-making, the study adds.
The review also cites evidence of changes in the hippocampus, a region important for memory, as well as disruption in connections between different areas of the brain.
In older adults, long-term exposure has been associated with reduced brain volume and impaired hippocampal function. At the same time, changes in the prefrontal cortex and increased white-matter abnormalities have also been reported.
The researchers caution that such findings should not be interpreted as proof that air pollution alone causes neurological diseases. Much of the existing evidence concerns structural and cognitive changes rather than confirmed cases of diseases such as Alzheimer’s or Parkinson’s.
The findings also raise particular concerns for children and young people because their brains are still developing.
The review cites studies reporting reduced grey and white matter volumes in children exposed to air pollution, along with possible effects on IQ, attention and behavioural regulation.
Research on prenatal and early-life exposure has also linked pollution exposure with impaired cognitive development and lower intelligence scores in children.
The review notes that early-life exposure can affect biological pathways involved in brain development and synaptic plasticity, the process through which connections between brain cells are formed and strengthened.
The concern is not limited to children. The review cites evidence of subclinical neurodegenerative changes in otherwise healthy young adults, suggesting that prolonged pollution exposure could potentially contribute to premature ageing of the brain.
According to the review, several processes may work together to cause the neurological effects.
PM2.5 exposure can activate microglia, the brain’s immune cells, leading to inflammation. Persistent inflammation can affect nerve cells and their connections.
Pollution can also cause oxidative stress, damaging proteins, fats and DNA, while affecting mitochondria, which provide energy to cells.
The hippocampus and prefrontal cortex may be particularly vulnerable because they have high energy requirements and play important roles in memory, learning and decision-making.
The review also highlights the role of metals and other toxic substances carried by particulate matter. These can interfere with communication between nerve cells and affect white matter development, particularly in the developing brain.
For Delhi, where exposure to particulate pollution can be a recurring part of daily life, the research adds another dimension to the city’s air pollution problem, suggesting that the impact of polluted air may not always be immediately visible and could extend to the brain over prolonged exposure.
