Air Pollution from Cars Tied to Dementia

An new study published this week in the National Institute of Health’s journal “Environmental Health Perspectives” has identified a very strong association between air pollution from automobiles and vascular and Alzheimer’s disease dementia. Dementia takes a heavy toll on the patient, the patient’s close relatives, and society as a whole, and is a growing concern as populations live longer.

The effects of air pollutants on heart, lung and circulation function are at this point well established. However, at this point there is growing evidence indicating that air pollution also causes cognitive effects and central nervous system disease. The number of studies suggesting an association between traffic pollution and cognitive function in adults is increasing. A study in Germany where the exposure to traffic-related particulates was estimated by the distance to the closest busy road, found an association between traffic-related particle exposure and mild cognitive impairment. In the Nurses’ Health Study Cognitive Cohort, which included 19,409 elderly women in the United States found that long-term exposure to particulates was found to be associated with faster cognitive decline, and a 10-μg/m3 increment in long-term particulate matter (both PM2.5 and PM2.5–10) exposure was cognitively equivalent to aging by approximately 2 years.

Particulate matter has immediate health impacts: itchy, watery eyes, increased respiratory symptoms such as irritation of the airways, coughing or difficulty breathing and aggravated asthma. However, in long term exposure to particulate pollution the particles can travel deep into the lungs, enter the bloodstream, and penetrate into cells. Particulate matter is made up of particles that are emitted directly, such as soot and dust, as well as secondary particles that are formed in the atmosphere from reactions of precursor pollutants such as oxides of nitrogen (NOx), sulfur oxides (SOx), volatile organic compounds (VOCs), and ammonia (NH3).

Particle are either directly emitted or formed in the atmosphere. Directly-emitted particles come from a variety of sources such as cars, trucks, buses, industrial facilities, power plants, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood. Other particles are formed indirectly when gases produced by fossil fuel combustion react with sunlight and water vapor. Many combustion sources, such as motor vehicles, power plants, and refineries both emit particles directly and emit precursor pollutants that form secondary particulates.

In the current study the researchers utilized the data in the longitudinal Betula study. Betula study was created and designed to explore various aspects of health and cognitive aging, including early signs of and potential risk factors for cognitive decline and dementia in adulthood and late life. Betula project studies lifestyle, environment, health and how memory functions change during adult life and old age, to identify risk factors for dementia and to identify early preclinical signs of dementia. The participants of the project have (so far) been tested, interviewed and examined medically on six occasions (1988-1990, 1993-1995, 1998-2000, 2003-2005, 2008-2010 and 2013-2014) in the past quarter century. The Betula study area is a small city in Sweden called Umea.

The study used the annual mean NOx concentration at the participant’s home address to represent the long term exposure to air pollution. The researcher found that the proportion of participants diagnosed with dementia increased with increasing NOx concentration at the participant’s homes. The model was adjusted for age and ApoE4, education, physical activity , smoking, sex, alcohol use BMI and still the data showed the correlation between air pollution and developing dementia. The presence of intermedate factors of hypertension, diabetes and stroke which are risk factors for dementia was also adjusted and still the proportion of participants diagnosed with dementia increased with increasing Nox concentration at the participants home.

Though Umea is a city with very low regional background levels of air pollution, there are still significant air pollution gradients within the city. Air pollution is hyper local and are tracked within the city and modeled. The major source of NOx pollution in the city is vehicle exhaust from local traffic. The results of the present study are a strong indication that air pollution may cause dementia and further research needs to be done. Meanwhile think about your own exposure to vehicle pollution. How's your air quality today?

Citation: Oudin A, Forsberg B, Nordin Adolfsson A, Lind N, Modig L, Nordin M,

Nordin S, Adolfsson R, Nilsson LG. 2016. Traffic-related air pollution and dementia incidence in northern Sweden: a longitudinal study. Environ Health Perspect 124:306–312;