(CNN) Levels of air pollution well below what is considered safe by the US Environmental Protection Agency and the World Health Organization are causing an increased risk of diabetes worldwide, according to a study published Friday in the journal Lancet Planetary Health.
In 2016 alone, the study found that air pollution contributed to 3.2 million new diabetes cases --14% of the total -- around the world. In the United States, air pollution was linked to 150,000 new cases of diabetes per year.
"There's an undeniable relationship between diabetes and and particle air pollution levels well below the current safe standards," said senior study author Dr. Ziyad Al-Aly, an assistant professor of medicine at Washington University. "Many industry lobbying groups argue that current levels are too stringent and should be relaxed. Evidence shows that current levels are still not sufficiently safe and need to be tightened."
Particulate or particle air pollution is made up of microscopic pieces of dust, dirt, smoke and soot mixed with liquid droplets. The finest particles regulated by the EPA are 2.5 micrometers; to put that in perspective, a strand of human hair is 70 micrometers, or more than 30 times larger.
Anything less than 10 micrometers can not only enter the lungs, it can pass into the bloodstream, where it is carried to various organs and begins a chronic inflammatory reaction thought to lead to disease.
"Ten or 15 years ago, we thought that air pollution caused pneumonia, asthma and bronchitis and not much more than that," said Dr. Philip Landrigan, dean for global health at Icahn School of Medicine at Mount Sinai in New York, who was not involved in the study. "We now know that air pollution is a very important cause of heart disease and stroke and contributes to chronic lung disease, lung cancer and chronic kidney disease."
Over 30 million Americans have diabetes, and the numbers worldwide are staggering: According to WHO, 422 million adults had been diagnosed by 2014, compared with 108 million in 1980. Low- and middle-income countries least able to manage the disease were experiencing the most growth.
While obesity, lack of exercise and genetic risk are major drivers for diabetes, studies have shown a link between the disease and pollution. Air pollution is thought to trigger inflammation and reduce the ability of the pancreas to manage insulin production.
In this study, researchers from the Washington University School of Medicine in St. Louis gathered data on 1.7 million US veterans with no history of diabetes who had been followed for a median of 8½ years. After controlling for all medically known causes of diabetes and running a series of statistical models, they compared the veterans' levels of diabetes to pollution levels documented by the EPA and NASA.
In veterans exposed to air pollution between 5 and 10 micrograms per cubic meter of air, much less than the EPA safe level of 12 micrograms, approximately 21% developed diabetes. Being exposed to higher levels, between 11.9 to 13.6 micrograms, created a greater risk: About 24% developed diabetes. Researchers point out that while the 3% increase appears small, it translates into an additional 5,000 to 6,000 new diabetes cases per 100,000 people each year.
Those data, along with information culled from thousands of studies worldwide, were used to create a model to evaluate diabetes risk across various pollution levels. Finally, those data were combined with information from the Global Burden of Disease study, which estimates annual cases of diabetes and healthy years of life lost due to pollution, to estimate risk worldwide.
Poorer countries with few resources to create and maintain clean-air policies, such as India, Afghanistan, Papua New Guinea and Guyana, faced a higher diabetes-pollution risk. Wealthier countries such as France, Finland and Iceland faced a low risk. The US faced a moderate risk.
"This is a very well-done report, very believable, and fits well with this emerging knowledge about the impacts of air pollution on a series of chronic diseases," Landrigan said. "I think you can very directly link relaxation of air pollution control standards with increased sickness and death."
Landrigan is a member of The Lancet Commission on pollution and health, which released a report last year estimating that pollution was responsible for 9 million premature deaths worldwide in 2015. That's 15 times more deaths than all wars and violence combined and three times more than malaria, tuberculosis and AIDS combined.
The commission said that 92% of pollution-related deaths occurred in low- and middle-income countries among minorities and the poor. Children, it said, are especially vulnerable, even to low-dose exposure.