A new global study links air pollution to an increased risk for type 2 diabetes – a troubling finding particularly for California's Central Valley, with its notoriously high levels of hazardous particulates.
Air pollution has long been widely known to pose a health threat: Consequences include asthma and other lung problems, and within the last decade, air pollution has been found to increase the risk for heart and kidney disease.
The new link to type 2 diabetes comes in a study published by The Lancet Planetary Health, looking at the global and national impact of air pollution-associated diabetes. Findings attribute 3.25 million newly diagnosed cases of type 2 diabetes internationally, in 2016 alone, to air pollution.
Dr. Ziyad Al-Aly, an author of the study as well as an assistant professor of medicine at Washington University at St. Louis, discussed the impact of breathing in air pollutants.
“We tell people all the time, if you eat bad stuff, it affects your health,” Al-Aly said. “You are what you eat, you are what you drink and, really, you are what you breathe. What you breathe really, really affects your health.”
Eight of the top ten cities in the U.S. that rank highest for short-term particle pollution are in California, according to the American Lung Association's 2018 State of the Air report. The top three cities in the nation are Bakersfield, Visalia and Fresno. And seven of the top 10 cities in the U.S. that rank highest for year-round particle pollution are in California.
Will Barrett, a manager of advocacy and clean air with the American Lung Association in California, explained that areas like San Joaquin County in California's Central Valley face unique challenges in efforts to reduce air pollution. Challenges include emissions from agriculture and trucks that drive through the Valley, pollution from wildfires and cases of extreme heat that can trap pollution for days.
Sacramento is ranked as one of the most polluted cities nationwide by the American Lung Association.
Previous research was done that hinted to a link between air pollution and type 2 diabetes. And while Al-Aly said this research hypothesized that a link existed, he and his colleagues were surprised by their findings.
“What we didn’t really know was the magnitude of the problem,” he said. “We were shocked by the magnitude.”
So what does air pollution have to do with type 2 diabetes? The association between the two is directly related to a tiny air particle referred to as particulate matter 2.5, dangerous both because it’s noxious and for its incredibly small size — less than 2.5 micrometers and naked to the human eye. The particle is significantly smaller than the diameter of a human hair.
PM 2.5 particles are released in the air as a result of emissions from cars, buses and factories. Al-Aly explained that these small, noxious particles enter the body and reduce its ability to respond to insulin.
These particles are so small, he said, that unlike larger particles that get stuck in the lungs and can be coughed up, PM 2.5 particles can penetrate through the lungs and end up in the bloodstream. From the bloodstream, these particles can go anywhere in the body, leading to severe health concerns.
"When you breathe in particles, you're putting your health at risk," Barrett said. "It hangs around and it does cause damage."
Dr. G. Prakasam, a local pediatric endocrinologist with Sutter Health, said unlike type 1 diabetes, which is caused by a body's lack of insulin, type 2 diabetes is characterized by the body's resistance to the insulin being produced. Exposure to air pollutants is directly related to decreased insulin sensitivity, according to evidence cited in the study.
According to the American Diabetes Association, insulin enables sugar, an important source of fuel for the body, to enter cells.
“Type 2 is looked at as the lesser type of diabetes,” Prakasam said. “But the long term complications are easily as bad as type 1.”
The study followed 1.7 million American veterans from Veterans Affairs for a median of 8.5 years. None of the participants had a prior history of diabetes and researchers set controls for factors including health behaviors, social and economic circumstances and physical environments.
After gathering data following the research population, researchers used data from the Environmental Protection Agency and NASA’s satellite sensing data for measuring levels of air pollution to define exposure of PM 2.5 across the participant population.
Researchers used these findings and the global burden of disease methodology, a measurement to estimate the impact of a disease, to examine how diabetes linked to air pollution affected 194 countries and territories.
Findings of the study showed 8.2 million years of healthy life were lost due to diabetes attributable to air pollution in 2016 globally. In addition, over 206,000 deaths from type 2 diabetes were linked to air pollution.
Countries found to have the highest attributable burden of death were China, India and the U.S.
With cases of type 2 diabetes increasing significantly, including among children, Prakasam said he would not be surprised to hear about the link between air pollution and an increased risk of type 2 diabetes since it’s still unclear why people are now at a higher risk of developing the health complication. If the study can be replicated three or four times, he said, there is a clear link.
Earlier this year, Sacramento County received an F score from the American Lung Association for both ozone levels and 24-hour particle pollution levels. According to the Sacramento Air Quality Management District, PM 2.5 is one of the region's top air pollutants, the other being ground-level ozone.
Al-Aly explained that of the measurements available for PM 2.5 levels, the most important is the annual average. The EPA designates safe levels at 12 micrograms per cubic meter of air, but the study found that levels below those explicitly identified by regulatory agencies may pose a risk.
"In our studies we observed that risk started to manifest at PM 2.5 concentrations above 2.4 microgram/cubic meter," Al-Aly said.
The annual average of PM 2.5 levels for Sacramento County from 2016, the most recent year available, shows 8.8 micrograms per cubic meter, according to kidsdata.org.
Barrett acknowledged that EPA standards are set at a level to protect public health, but health officials recognize that particle levels in smaller amounts pose a health threat. Barrett said standards should be reviewed annually and based on the best science available.
Sacramento County ranked 19 among U.S. cities for unhealthy air in 2018, but the region has already seen improvements in air quality.
"We've made tremendous progress," Barrett said, explaining that the county has seen an 80 percent reduction in the number of unhealthy particle pollution days since 2004. This reduction is due to factors including cleaner vehicle standards and the local Check Before you Burn program for controlling wood smoke.
The study outlines other health consequences posed by exposure to air pollution, including inflammation and complications in the autonomic nervous system, which controls unconscious bodily functions like heartbeats and breathing.
"There is really no safe level of particle pollution," Barrett said. "Our lungs were not intended to breathe polluted air."