Air pollution is “likely” to increase the risk of developing dementia, a Government research group has said.

The Committee on the Medical Effects of Air Pollutants has published its findings after reviewing almost 70 studies which analysed how exposure to emissions affects the brain over time.

The 291-page report concludes that air pollution “likely” increases the risk of accelerated “cognitive decline” and of “developing dementia” in older people.

Experts believe this is due to the impact of pollutants entering the circulatory system, affecting blood flow to the brain.

In a statement, the authors said: “The epidemiological evidence reviewed fairly consistently reports associations between chronic exposure to air pollution and reduced global cognition and impairment in visuospatial abilities as well as cognitive decline and increased risk of dementia.

“Results are heterogeneous as regards to other cognitive domains such as executive function, attention, memory, language and mild cognitive impairment.

“The identified neuroimaging studies consistently report associations between exposure to air pollution and white matter atrophy.”

It is not certain exactly which pollutant causes these effects.

There is also more well-established evidence to show that exposure to air pollution increases the risk of heart disease.

Breathing in emissions can damage the blood vessels by making them narrower and harder – increasing the likelihood of clots, abnormal heart rhythms and heart attacks, according to the British Heart Foundation.

The committee said it has made recommendations for further research to help develop the evidence.