Australian researchers have found a clear link between air pollution and an increased risk of developing dementia later in life, in a study that pulls together global data for the first time.
The study, printed in the Journal of Alzheimer’s Disease, analyses research on people living in regions of Canada, Sweden, Taiwan, the United Kingdom and the United States.
It shows higher rates of dementia when people were exposed over a long period of time to two types of air pollutants commonly found in cities worldwide. These are nitrous oxides and particulate matter 2.5 – an airborne mix of solid particles and liquid droplets where each particle is less than 2.5 micrometres wide (the average human hair is 70 micrometres wide).
Study author Dr Ruth Peters at Neuroscience Research Australia (NeuRA) says the research raises a warning flag.
“This study finds mounting evidence that air pollution increases the risk of dementia and cognitive decline later in life,” she told Community Care Review.
“This is something we need to be aware or and we need to look into in more detail so we can understand what the different levels of pollution are doing to us, and how much each pollutant – or each combination of pollutants – matters. Then we can really understand what recommendations to make.”
Researchers believe air pollutants may lead to an increased risk of dementia by increasing levels of inflammation in our bodies and by raising the risk of having a stroke. The rate of developing dementia is 50 times higher in the year after a major stroke.
Increased risk in low-income countries
The study pulls data from high-income countries. In low- and middle-income countries, Dr Peters believes the link between air pollution and dementia rates could be even higher.
“We know there are going to be a lot of dementia cases in these countries because of the ageing populations but we also know that the higher polluting areas are more likely to be within those countries,” she said. “So we need to do that additional investigation to understand what’s happening in those areas.”
Research over the last decade has shown that the risk of developing dementia later in life can be determined by factors that play out throughout the entire life course.
But while we may be able to actively reduce those risks by keeping blood pressure down, following a healthy diet, maintaining a healthy weight and exercising, says Dr Peters, we can’t all move to a mountain.
“It is very difficult for someone to reduce their exposure to air pollution, especially if they live somewhere where pollution levels are high,” she said.
This is “concerning”, she added, given the World Health Organisation estimates 91 per cent of the of the world’s population lives in places where air quality exceeds its guideline limits.
Dr Peters says the study highlights the need for further research to understand the impact of different pollution levels in rural, industrial and city environments in order to make specific guidelines and recommendations at both the national and global level.
“Research shows that government regulation that reduces our exposure to air pollution has a huge potential health and economic benefit,” she said.