New study reveals surprising factor that could increase risk of disease that impacts millions of Americans

A new study has identified a major factor that can increase the risk of dementia by up to 17 percent.

The disease impacts around six million people in the US, with that figure expected to rise to 12.7 million by 2050, according to the Alzheimer's Association.

The condition is characterized by 'progressive or persistent' loss of intellectual functioning, which impacts memory, abstract thinking and even causes personality changes.

Symptoms could manifest as being unable to learn new tasks, struggling to stay focused, finding it hard to contribute in conversations, mistaking things for other objects and/or getting unusually emotional or afraid.

And now, University of Cambridge scientists have found that our environment could increase our risk of developing dementia, making a surprising link between air pollution and the disease.

Dementia impacts around six million Americans (Tek Image/Science Photo Library/Getty Images)

Data from some 29 million dementia patients were analyzed as part of the study, published in The Lancet Planetary Health.

In total, 51 studies were probed, mostly from high-income countries in North America, Europe, Asia and Australia.

What did the study find?

The research uncovered that there are three types of air pollution that can increase the risk of developing the disease by varying percentages.

PM2.5

One type is PM2.5 - particulate matter with a diameter of 2.5 microns or less. Basically, tiny particles in the air, from cars, factories and fires.

These can travel far, stay in the air for a long time and get deep into people's lungs.

The dementia risk increases by up to 17 percent for every 10 micrograms per cubic meter (µg/m³) of this type of pollution.

At the time of writing, according to Aqicn.org, the maximum PM2.5 levels in New York is 156.

Nitrogen dioxide

Being exposed to certain air pollution long-term can increase risk of dementia (Connect Images RF/Ditto/Getty Images)

Another is nitrogen dioxide, or NO2 - a gas from burning fuels like car engines, gas stoves and power plants.

It can irritate people's lungs and worsen asthma. The dementia risk increases by three percent for every 10 µg/m³.

The maximum measurement in New York, as per Aqicn, is 23.

Soot

Then there's soot, black particles from exhausts and wood burning. It harms the lungs and heart, while trapping heat - meaning it also harms the environment.

The dementia risk is 13 percent for every 1 µg/m³ of soot, the study found.

What did the authors of the study say?

The University of Cambridge conducted the research across 30 million dementia patients (Andrew Holt/Getty Images)

Senior author Dr Haneen Khreis, from the MRC Epidemiology Unit, said: "Our work provides further evidence to support the observation that long-term exposure to outdoor air pollution is a risk factor for the onset of dementia in previously healthy adults.

"Tackling air pollution can deliver long-term health, social, climate, and economic benefits. It can reduce the immense burden on patients, families, and caregivers, while easing pressure on overstretched healthcare systems."

Joint first author Clare Rogowski, also from the MRC Epidemiology Unit, added: "Efforts to reduce exposure to these key pollutants are likely to help reduce the burden of dementia on society.

"Stricter limits for several pollutants are likely to be necessary targeting major contributors such as the transport and industry sectors.

"Given the extent of air pollution, there is an urgent need for regional, national and international policy interventions to combat air pollution equitably."