New research has estimated hundreds of thousands of cases of dementia in the US may be caused due to the air we are breathing in. As we live longer, more and more countries are battling with growing rates of dementia. Almost 188,000 dementia cases in the US each year are thought to be caused by air pollution, with poor air quality due to wildfires and agriculture showing the strongest association with an increased risk of Alzheimer's disease and other types of dementia later in life. The research , published Monday, August 14, in the journal JAMA Network Open, contains new estimates which are the latest to underscore a range of health risks long warned to be linked to air pollution. Studies have already linked poor air quality to a number of health problems, including the risk of developing dementia. However, the new study took a closer look at how specific causes of air pollution seem to be more strongly linked to dementia than others. For all the latest on news, politics, sports, and showbiz from the USA, go to The Mirror US . Living in cities could pose a risk of increased chances of developing dementia later in life ( Image: Getty Images) Findings were based on analysis of data collected from a decades-long survey, backed by the National Institutes of Health. Thousands of older adults were checked in with regularly every two years about their health. Researchers then combined that data with detailed air quality modelling, estimating what people may have been exposed to in the areas where they lived. The focus was on what scientists call PM 2.5 air pollution which is a benchmark for very small particles - less than 2.5 micrometres wide, a fraction of the diameter of human hair - that can be inhaled from the air. These particles can come from a variety of sources, including vehicle exhausts and wildfire smoke. They are linked to health effects which range from coughing or shortness of breath, to worsening asthma and even an increased risk of death from heart disease. Associate chair of epidemiology at the University of Michigan's School of Public Health, Sara Adar, said: "The environmental community has been working very hard for the past 10 to 15 years to be able to predict exposures." A range of data was drawn on, including measurements from the Environmental Protection Agency and details about nearby factors that could affect air quality - such as the recent wildfires in Canada which caused air quality warnings to be triggered across major US cities. "They model all sources at once. Coal-fired power plants, agriculture, wildfires, traffic, all these different emission sources, and then they turn off the source in the model one at a time. And then they can see the difference in what levels are there with the emissions sources, and what are there without them," said Dr Adar. The study followed adults for a number of years, checking in regularly to see how their health and mental function were ( Image: Getty Images/Image Source) Modelling found the higher risk even after adjusting for a range of potential other factors would could impact results, such as sex, race and ethnicity, educational status and wealth. They were also able to adjust for whether people have previously lived in urban or rural areas. While they had information about where people moved during the course of the survey, Dr Adar acknowledge they didn't have enough data to model every single exposure or check for every difference throughout the course of their life, such as where people were born, which could have impacted results. "Dementia takes a long time to develop," said Dr Adar. "It's not something that might be, 'oh you've got a bad exposure last week, and now you have dementia'. It's more likely to build up over a lifetime." Beyond direct emissions from wildfires and agriculture, Dr Adar said their analysis was able to take into account other kinds of air pollution that can also be traced back to these sources. When wildfires burn it isn't just the smoke that fills the air people have to worry about. Other toxic molecules can be carried with the smoke as they burn through communities. Farming can also worsen air pollution, as a result of ammonia released by sources like manure and fertiliser. "Farms will release a lot of ammonia gas, and then in the air with the sunlight and other pollutants out there, they'll react to make particles, and those particles are what we see are likely toxins for the brain," said Dr Adar. Dr Adar and Boya Zhang, a fellow researcher at the school, say they hope their new findings could help drive more targeted interventions to address dementia risks. The study's authors wrote: "Unlike many other common risk factors for dementia (eg. hypertension, stroke, and diabetes), exposures to air pollution can be modified at the population level, making it a prime target for large-scale prevention efforts."