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Air pollution and brain health, is it all smoke and mirrors?

You may have read news stories about a link between air pollution and neurodegenerative conditions like Alzheimer’s disease.

And in a landmark study published in The Lancet, air pollution was named as one of 12 important ‘modifiable’ risk factors for dementia. But what’s the nature of this link?

Does higher exposure to air pollutants lead to an increased risk of dementia?

Air pollutants are tiny particles and gases in the air that come from burning fossil fuels or from vehicle exhausts.

There’s a lot of research interest in where people live, including how close they are to major roads and whether this affects dementia risk.

In one important study, researchers in Canada looked at 6.6 million people, using their postcodes to measure how close they lived to major roads and their medical records to identify residents who had gone on to develop dementia.

This study, and others since, have suggested that living in an area with higher levels of air pollution is linked to an increased risk of developing dementia.

But it’s difficult to tease apart cause and effect.

Many factors including our age, genetics, and other health conditions all combine to shape our dementia risk, so it’s extremely hard to isolate the impact of a single factor like air pollution. More research is needed to further explore the link between living in areas of high pollution and dementia risk.

So, what could be behind this link?

Scientists are also exploring different biological links between air pollution and dementia.

Last year a team from the suggested that people who lived in areas of high air pollution had increased levels of amyloid  a protein associated with Alzheimer’s disease, in their blood,. Although this association between  air pollution and amyloid isn’t new, this study looked at exposure to air pollution over many years rather than at a single point in time.

Other processes being looked at include oxidative stress and brain inflammation.

Air pollutants are strong oxidising agents meaning they can react readily with other chemicals. This could lead to ‘oxidative stress’ – an imbalance between toxic molecules inside our cells and the antioxidants we need to remove them. This has itself been connected to the onset of dementia.

Brain inflammation is the immune system’s natural response to protect us from disease in the brain. In some cases, this response can become overactive and cause damage to healthy brain cells. In 2008, researchers in Mexico reported that people in high-pollution areas showed higher levels of brain inflammation compared to those in areas with lower pollution.

And it could be that air pollution has an indirect link with dementia through how it can impact our heart health. Several studies have linked exposure to air pollutants with restricted blood-flow in arteries which can lead to higher blood pressure and an increased risk of stroke – both risk factors for dementia.

Positively, further evidence suggests that reducing pollutants could help long-term brain health. Researchers saw an improvement in air quality in the US between 1996 and 2012 and think this contributed to a slower than expected decline in brain function seen in women across the US.

Taking action

As individuals, we can all take steps to help protect our brains – including regularly challenging them, looking after our hearts and keeping connected to the people around us. But there is less we can do about the air we breathe.

This is where working with policy makers is crucial. That’s why we have recently joined the Healthy Air Campaign, a coalition of charities seeking to improve air quality. As the relationship between air pollution and dementia risk is fairly new, we will need time to see how policy decisions will impact on brain health, however working towards cleaner air across the country is an important public health goal for us all.

 

About the author

Quang Tran

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