March 30 (UPI) -- Long-term exposure to air pollution may increase a person's risk for developing dementia, an analysis published Monday by JAMA Neurology has found.
In nearly 3,000 older adults in Stockholm, Sweden, researchers found the risk for declines in memory, language, problem-solving and other thinking skills dropped by as much as 50 percent for every five years of exposure to pollution, based on levels of particulate matter and nitrogen oxide in the air near their place of residence.
The air pollution-linked risk for dementia was even higher among those with a history of heart failure and ischemic heart disease, or stroke, the authors found.
"Air pollution has well-established repercussions on humans' health, in particular for what concern pulmonary diseases and cardiovascular morbidity," study co-author Giulia Grande, a researcher in neurobiology, care sciences and society at the Karolinska Institutet in Sweden, told UPI. "We have found, in line with other groups, that higher levels of air pollution were associated with increased dementia risk. More interestingly, we observed that half of the cases of dementia related to air pollution were explained by the development of stroke."
According to the Alzheimer's Association, nearly 6 million people in the United States are living with some form of dementia. The U.S. Environmental Protection Agency notes that, despite progress since 1970, air pollution continues to harm people's health and the environment in many parts of the country.
Using data gathered on adults age 60 years and older as part of the Swedish National Study on Aging and Care, Grande and her colleagues tracked the health of 2,927 people over a 20-year period against the levels of air pollution in the areas in which they lived. They found that every 0.88 micrograms per cubic meter rise in particulate matter in the air -- levels above 35 micrograms per cubic meter are considered dangerous -- an individual's risk for dementia increases by more than 50 percent.
Similarly, for every 8.35 microgram-per-cubic meter rise in nitrogen oxide levels in their air, an individual's risk for dementia increased by more than 10 percent. Among those with a history of heart failure or heart disease, long-term exposure to air pollution nearly doubled the risk for dementia.
"Our results derive from a central area of Stockholm, where the control of environmental air pollution has been increasingly strict in the last decades," Grande said. "Interestingly, the higher limit that we reported is not only below the current European limit for fine particulate matter but also below the U.S. standard. In other words, we were able to establish harmful effects at levels below current standards. Next time air quality standards are revised, this risk should also be considered."