Dementia takes hold when cognitive functions become disturbed. Does where you live increase your risk of the degenerative brain disease?
Researchers conducted an 11-year study to find out if where somebody lives could impact a person's risk of developing dementia.
Around 2,900 older people were involved in the study who lived in Sweden.
In particular, the participants were from one part of central Stockholm – an area where pollution levels are below the EU's safe limits.
Out of 2,900 people in the study, 364 of them developed dementia.
Air pollutants – namely nitrogen oxides and PM2.5 – were estimated at the residential addresses of those in the study.
The Environmental Protection Agency (EPA) details the dangers of nitrogen dioxide (NO2) – which is part of a group of gases called nitrogen oxides.
Released into the air from burning fuel (such as vehicle emissions), NO2 can irritate the airways in the human respiratory system.
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It can cause respiratory symptoms such as coughing, wheezing or difficulty breathing.
And, over a length of time, can lead to hospital admissions.
Moreover, EPA state PM2.5 (Particle Matter Pollution) are microscopic particles formed as a result of complex reactions between other air pollutants.
PM2.5 can enter people's lungs and bloodstreams causing damage to the body.DON'T MISS
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The researchers concluded in the Jama Neurology journal that older people exposed to air pollution are more at risk of dementia.
This is especially true if they suffer from cardiovascular disease.
Cardiovascular diseases affect the heart or blood vessels, such as heart disease or stroke.
Author Giulia Grande, researcher at the Department of Neurobiology, Care Sciences and Society at Karolinska Institutet, Stockholm, said: "Interestingly, we were able to establish harmful effects on human health at levels below current air pollution standards."
She continued: "Our findings suggest air pollution does play a role in the development of dementia.
"Mainly through the intermediate step of cardiovascular disease and stroke."
Taking the results further, Grande said: "In our study, virtually all of the association of air pollution with dementia seemed to be through the presence or the development of [cardiovascular diseases]."
And the researchers are adamant that "air pollution is an established risk factor for cardiovascular health".
These results imply living in polluted cities puts a person at an increased risk of developing dementia.
Dr Alison Evans, head of policy at Alzheimer's Research UK, supports this theory.
Dr Evans commented: "The brain is closely linked to the health of our heart and blood supply.
"In this well-conducted study, many of the dementia cases were linked to heart disease and poor brain blood supply.
"Good brain health should be a focus throughout life in order to reduce the risk of dementia.
"Working towards cleaner air in our cities should remain a critical public health goal."