Research in London links air pollution to dementia risk

BMJ Open: Are noise and air pollution related to the incidence of dementia? A cohort study in London, England

Researchers in the UK have found that increased levels of air pollution, including high levels of nitrogen dioxide and microscopic atmospheric particles called particulates, are associated with an increased risk of dementia. The findings have been published today (18 September) in the scientific journal, BMJ Open.

There are 850,000 people living with dementia in the UK and with age the biggest risk factor for the condition, this number is set to rise. The new study adds to previous research by Canadian scientists who identified a potential link between pollution, living near a major road and an increased dementia risk.

In this study, researchers looked at data from over 130,000 people, between the ages of 50 and 79, who lived within the M25 in Greater London and who did not have a dementia diagnosis at the beginning of the study in 2005. They followed these people for an average of 6.9 years to see if they went on to get a dementia diagnosis. They found that 1.7% of the people involved in the study were diagnosed with dementia within this follow up period.

Scientists calculated the levels of pollutants including nitrogen dioxide, particulates, ozone and night-time noise pollution in individual London postcodes every year from 2004 until 2010. Then, by collecting carefully anonymised information about the addresses of people who received a dementia diagnosis, the researchers compared diagnosis rates to the level of air pollution in different areas.

They found that living in one of the areas of London with the highest levels of nitrogen dioxide pollution was associated with a 40% higher risk of dementia than living in one of the least polluted parts of the city. They also found that dementia risk was increased in areas with higher levels particulates in the air.

The increased risk of dementia was found to be independent of other known risk factors for the condition such as age, sex, ethnicity, smoking, and importantly socioeconomic factors, which can be vastly different depending on location.

Interestingly when the researchers tried to take an even closer look at their results, drilling down to a disease specific diagnosis, they found that there was an association between a diagnosis of Alzheimer’s disease and increased air pollution, but this was not the case for a diagnosis of vascular dementia.

Dr David Reynolds, Chief Scientific Officer at Alzheimer’s Research UK, said:

“Dementia isn’t an inevitable part of getting older but is caused by a complex mix of age, genetics and environmental factors. With one in three people born today set to develop dementia in their lifetime, there is a pressing need to identify and understand potential risk factors for the condition. This large, well-conducted study highlights an association between dementia risk and local levels of air pollution, but we can’t be sure of cause and effect in this relationship.

“While the researchers tried to account for factors like wealth, heart disease, and other potential explanations for differences in dementia rates across the capital, it is difficult rule out other explanations for the findings. The research relies on diagnosis rates, which don’t always accurately reflect the number of people living with dementia and that we know can vary between GP practices and health trusts.

“The diseases that cause dementia can begin in the brain up to twenty years before symptoms start to show. We don’t know where people in this study lived in the two decades before their dementia diagnosis, so we have to be cautious about how we interpret these results.

“The link between air pollution and dementia risk is a growing area of research. This study highlights the importance of further studies that look into exposure to pollution over a longer period of time, and investigate the possible biological mechanisms underlying this link. While research in this area continues, air pollution can impact a number of different aspects of our health and working towards cleaner air in our cities should be an important public health goal.”