People over age 50 who live in areas with the highest levels of air pollution, specifically nitrogen dioxide, the byproduct of traffic emissions, were more likely to develop dementia than those living in areas with the lowest levels. That’s according to an observational study published online in BMJ Open on September 18.
A team of researchers studied data from a database that has been collecting anonymous patient information from participating general practitioner (GP) offices in the UK since 1987. The researchers linked records of 130,978 adults aged 50 to 79 to data on air pollution from monitoring sites closest to the patients' residential postcodes.
The researchers observed pollution data from 2004 and patient records from 2005 to 2013. In the study, patients had no documented history of dementia or residence in a nursing home. They were followed until the end of the study, until they had a diagnosis, or until they died or moved away from their GP.
Pollutants monitored in the study included nitrogen dioxide, fine particulate matter—small particles that can affect the heart and lungs—and ozone. The researchers assessed traffic density or participants’ proximity to heavy traffic and road noise to quantify noise pollution.
Over the span of seven years, 2,181 patients were diagnosed with dementia; 39 percent Alzheimer's disease, 29 percent vascular dementia.
The researchers found older people living in the areas most polluted with NO2 were 40 percent more likely to be diagnosed with dementia than those living in the areas with the lowest amount of pollution. Those living in areas most polluted with fine particulate matter from traffic were 26 percent more likely to have been diagnosed with dementia. Other types of pollution, like noise pollution, were less strongly linked to a dementia diagnosis.
In an attempt to quantify the risk, the researchers calculated that if all participants had been exposed to the same levels of NO2 as those in the least polluted areas, about 7 percent of dementia cases may have been prevented.
The findings add to a growing body of evidence linking air pollution and neurodegeneration, the researchers concluded.
The study does not prove air pollution causes an increased risk of dementia, but the findings, if true, have significant public health consequences, the researchers wrote—even if cleaner air only delayed the progression of dementia.
The researchers say more research is needed to explore the link between air pollution and dementia since pollution exposure is lifelong and most dementia cases are diagnosed later in life.