Scientists find shocking cause of cancers plaguing more than 70,000 Americans each year

Scientists have uncovered a shocking link between air pollution and a group of cancers that plagues tens of thousands of Americans each year. 

The researchers found that exposure to PM2.5 pollution - or particulate matter smaller than 2.5 microns - increases the risk of head and neck cancers (HNC). 

Common types of HNC include throat cancer and mouth cancer, which an estimated 71,100 Americans will be diagnosed with in 2024.

The study discovered that breathing in PM2.5 increased the risk of developing HNC by 24 percent five years after exposure to this pollutant. 

Even within just one year of PM2.5 exposure, the researchers found that the risk of developing HNC increased by 16 percent. 

PM2.5 is generated through a variety of industrial processes, including fuel burning and manufacturing, but can be generated inside the home by burning candles, using certain cleaners or air fresheners, and other activities. 

Particulate matter can be found all across the US, but PM2.5 pollution is particularly severe in states such as California, Georgia and Utah.

Studies have shown that HNC rates are particularly high in the Midwest and Southeast. These regional economies rely heavily on manufacturing, agriculture and energy, all of which are key producers of air pollution. 

The harmful effects of particulate matter on human health - including increased risk of cancer - has been well documented. 

But now, researchers have investigated how breathing in PM2.5 specifically affects the risk of developing HNC.

'Environmental health and personal health are inextricably linked,' said co-author Dr Amanda Dilger of the Center for Surgery and Public Health and Massachusetts Eye and Ear, in a statement. 

Dilger and her colleagues published their findings in the journal Scientific Reports on November 12. 

The research team, which spanned several US research hospitals, gathered data from the Surveillance, Epidemiology, and End Results (SEER) national cancer database.

The SEER database tracks cancer cases and collects follow-up information on all previously diagnosed patients until their death.

The researchers pulled data on HNC cases spanning 2002 to 2012, and then linked those cases to county-level data on PM2.5 pollution, alcohol use and smoking across all available years.

The cohort included cancer cases from California, Connecticut, Southeast Michigan, Georgia, Iowa, Kentucky, Louisiana, New Jersey, New Mexico, Seattle (Puget Sound) and Utah. 

Patients had been diagnosed with oral cavity, oropharynx, larynx, hypopharynx, sinonasal and middle ear cancers.

The analysis found a significant association between PM2.5 levels and the incidence rate of HNC, and this relationship was strongest at a five-year lag period. 

This means that the risk of developing HNC increased the most at five years after exposure to PM2.5 pollution - rising by 24 percent. 

But PM2.5 exposure also increased HNC risk over shorter and longer time periods.

At the time of exposure (AKA a zero-year lag) HNC risk increased 16 percent, and after 20 years, the risk increased 15 percent. 

'These findings shed light on the significant role of environmental pollution in cancers of the upper aerodigestive tract, highlighting the need for further awareness, research and mitigation efforts,' said Dr Stella Lee, study senior author and rhinologist Brigham and Women's Hospital, in a statement. 

While the link between PM2.5 exposure and HNC has been historically understudied, according to the researchers, it's well-known that this type of air pollution is a powerful carcinogen. 

The International Agency for Research on Cancer (IARC) classifies air pollution, particularly PM2.5, as a carcinogen known to cause cancer in humans - particularly lung cancer. 

But cells in the head and neck are especially vulnerable to air pollution. 

'Presumably, the link to head and neck cancer comes from what we breathe to that material affecting the lining in the head and neck,' said lead author Dr John Cramer, associate professor of otolaryngology at Wayne State University in Detroit.  

'We see a lot of occurrences of where carcinogens touch or pool in the body to where cancers can occur,' Cramer added.

But breathing air pollution can lead to other health risks too. This study comes on the heels of research that uncovered a link between air pollution exposure and higher  incidence of miscarriage in Baoji, China. 

There are several theories for why air pollution may cause miscarriage, including disruption of pregnancy hormones, triggering harmful inflammation in the mother and negative impacts on fetal development.

As researchers dive deeper into the many ways that air pollution harms human health, they are also pushing for improved air quality standards to mitigate the affects of these harmful substances. 

'Our study highlights the need to improve air quality standards in order to decrease the risk of developing cancer, including head and neck cancer,' Dr Dilger said.