Tiny particles breathed in and taken into the brain through air pollution could be linked to diseases such as Alzheimer's, research has found.
Experts have discovered the presence of magnetic nanoparticles, which have previously been associated with the development of neurodegenerative diseases such as Alzheimer's, in the human brain.
According to researchers from the UK and Mexico, the shape and features of the nanoparticles suggest they are less likely to have been formed naturally in the body and more likely to have come from an outside source, possibly air pollution.
Alzheimer's disease is caused by a build-up of proteins in the brain, leading to the loss of brain tissue, the death of nerve cells and a shortage of important brain chemicals.
It is a common cause of dementia and affects more than 520,000 people in the country, the Alzheimer's Society website says.
Researchers have said they cannot say for sure whether there is a causal link between these nanoparticles and Alzheimer's.
Dr David Reynolds, chief scientific officer at Alzheimer's Research UK, said: "Little is known about the role of magnetite nanoparticles in the brain and whether their magnetic properties influence brain function.
"It's interesting to see further research investigating the presence of this mineral in the brain, but it's too early to conclude that it may have a causal role in Alzheimer's disease or any other brain disease.
"We know that air pollution can have a negative impact on certain aspects of human health, but we can't conclude from this study that magnetite nanoparticles carried in air pollution are harmful to brain health."
He highlighted the fact that, while it is important to continue to study the impact of lifestyle and environment on brain health, age and genetic risk factors also play a role in influencing a person's risk of Alzheimer's.
The findings are published in the journal Proceedings of the National Academy of Sciences.