Air pollution in big cities increases the risk of Alzheimer's in children and young adults, according to a study conducted by researchers at the University of Montana.

Subjects in the study ranged in age from 11 months to 40 years, and researchers found signs of Alzheimer's in 99.5 percent of them, including in less-than-a-year-old infants.

The study discovered that people living in highly polluted areas develop high levels of hyperphosphoryl tau and beta amyloid proteins in their brains, which eventually increases the risk of getting Alzheimer's disease.

Researchers theorized that particulate matter increased Alzheimer's risk as it enters the brain through the gastrointestinal tract, nose and lungs. The circulatory system carries particulate matter throughout the body and damages barriers.

According to a write up of the study in Popular Science, living in areas with high air pollution has been linked to poor memory, lower intelligence-test performance and behavioral problems.