POLLUTION REVS UP RISK
by Dan Birch
If there were not already enough reasons to put the brakes on environmental air pollution, another concern looks to be rounding the bend.
Recent research out of Children’s Hospital Boston, funded by the National Institutes of Health in Bethesda, Maryland, is lending credence to the theory that pollution is a risk factor for diabetes. Particulate matter pollution, especially when particulate is between 0.1 and 2.5 microns in size (PM2.5), “may be a neglected risk factor for diabetes,” writes John Pearson, lead author of the study that appeared last October in the journal, Diabetes Care.
Sources of “fine” particles include combustion, such as that related to motor vehicles, power plants, residential wood burning, forest fires, agricultural burning and some industrial processes, reports the U.S. Environmental Protection Agency (EPA) in Washington, D.C.
Pearson notes that “as a main component of haze, smoke and motor vehicle exhaust, PM2.5 is dangerous, in part, because of its small size and ability to invade critical human organs in the respiratory and vascular systems.”
The study’s research team assessed statistical models that made use of data from the Centers for Disease Control and Prevention in Atlanta and the EPA. It found that for every 10 micrograms per cubic metre increase in PM2.5 exposure, there was a one per cent hike in diabetes prevalence.
As well, the team identified higher prevalence for geographic areas that were below EPA legal limits for PM2.5 air pollution. “Populations living in areas that are near, but still below, the EPA limits show [a greater than] 20 per cent higher diabetes prevalence compared with those in cleaner areas,” Pearson writes.
In an interview, he says that the study does not demonstrate definitively that PM2.5 causes diabetes. “We can’t say if it is causal, based on our model, but it seems to be pointing in that direction,” he says, adding that other research shows an increase in insulin resistance – a precursor to diabetes – in obese mice exposed to particulates.
Pearson writes that the PM2.5 study findings “are consistent with the few studies of geographically small areas that have also suggested a relationship between diabetes and air pollution from either road traffic or industrial facilities.”
Taken together, those studies suggest obesity may play a critical permissive role in priming the body for pollution-induced inflammation and disordered metabolism. But, Pearson notes, more research is needed to “understand the role that PM2.5 plays in the inflammatory pathway or other pollution-mediated mechanisms giving rise to diabetes.”
The possible diabetes-air pollution link is “quite fascinating,” says John Oudyk, a registered occupational hygienist with the Occupational Health Clinics for Ontario Workers Inc. (OHCOW). “We know that reducing air pollution is beneficial to outdoor workers,” says Oudyk, who works out of OHCOW’s office in Hamilton, Ontario. But other reasons to tackle air quality include lung and cardiovascular illness.
Information from Health Canada in Ottawa notes that the “health effects caused by air pollutants may range from subtle biochemical and physiological changes to difficulty breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions.”
Just as diabetes is but one health concern associated with air pollution, dirty air represents a relatively small risk factor for diabetes compared with others.
Dr. Robert Brook, associate professor in the Department of Internal Medicine at the University of Michigan in Ann Arbor, has explored the emerging link and reports that air pollution is much less of a diabetes risk factor than contributors such as “age, race, family history and obesity, excess calories, high sugar [and] lack of exercise.”
That said, air pollution is still an issue “because the small increase in risk for each individual is magnified over a huge population in modern society. Thus, for the larger public health, there is a significant effect,” says Dr. Brook, who partnered with other researchers on a study in the Journal of Occupational and Environmental Medicine (JOEM) in 2008.
But how exactly does air pollution influence diabetes, a disease caused by insufficient insulin production and the body’s ineffective use of insulin?
“The inhalation of particles causes inflammation in the lung. Certain factors [or] mediators that convey inflammation spill over into the whole body,” via the circulatory system, Dr. Brook explains. “Many of these factors – for example, cytokines – are known to impair the action of insulin and, thereby, lead to insulin resistance, high blood sugar and over time, promote diabetes mellitus,” he notes.
In addition, Dr. Brook points out, particle inhalation disrupts the autonomic nervous system, and chemicals on inhaled particles might leach off and enter the blood.
Pearson says that some particulates become trapped in the lungs, “messing up the communication between insulin, muscle and fat, which translates to insulin resistance.”
The JOEM study made use of data from patients aged 40 and older at respiratory clinics in Toronto and Hamilton. It found that exposure to nitrogen dioxide, a marker of traffic-related air pollutants, was associated with diabetes prevalence in women. The same conclusion was not reached for men, although Dr. Brook and his colleagues suspect that exposure estimate errors may account for the difference.
The growing body of research on diabetes and air pollution has captured the attention of the American Heart Association in Dallas. In the association’s journal, Circulation, a 2009 editorial by Aruni Bhatnagar, Ph.D., notes that “an emerging paradigm is that immunity and metabolism are inextricably linked. Because energy is required to fight infection, starvation suppresses immune response.”
Inflammation and infection both favour “catabolism and down-regulate anabolic signals such as those triggered by insulin,” Dr. Bhatnagar writes. “This paradigm offers a new perspective, which suggests that pollutant exposure, when superimposed on diabetes and obesity, could further aggravate the energy mismatch by triggering immune responses and inducing inflammation,” he notes.
The paradigm raises important questions, Dr. Bhatnagar says. “To what extent does pollution contribute to the current explosion in diabetes and obesity in the developed and the developing world? Can we prevent diabetes by controlling the levels of pollution? And if so, which of the thousands of chemicals in [particulate matter] should be regulated?”
Workers labouring in areas where there is heavy traffic and high ambient air pollution should take note, Pearson suggests. Care is also necessary to minimize exposure to indoor air pollution, which can come from printers, fax machines and other peripherals, he says. Limiting exposure by having the machines in isolated rooms is advisable.
It is “a challenge for employers to protect against general air pollution, but employers can help by minimizing exposures to pollutants at work that they can control,” says Andrew Ross, manager of health and safety for the City of Vancouver. “Minimizing the burden on the lungs at work is an important part of protecting workers’ health [against] general air pollution,” adds Ross, who reports that compensation claims related to exposure for municipal employees cite specific workplace conditions rather than general air pollution.
Consideration of work rates is also crucial when air quality deteriorates, Oudyk says. “If you’re working extremely hard, you’re breathing harder and, therefore, you’re taking in a lot more pollutants,” he notes.
Taking things easy when the air is bad is a familiar message, oftentimes delivered by public health agencies in the dog days of summer. Also familiar is the refrain for vulnerable individuals – such as workers with asthma or cardiovascular disease – to be cautious.
Workers in construction, trucking and other transportation operations are “likely to have higher [particulate matter] exposures” than the general population, says Michael Brauer, a professor at the University of British Columbia’s School of Environmental Health in Vancouver, and director of the university’s interdisciplinary Bridge Program.
Particulate-blocking gear, such as an N95 respirator, may be one protective option. Dr. Brook points to evidence out of Beijing that indicates wearing a mask while walking through the city can prevent increases in blood pressure. For those with heart disease, wearing the equipment can also maintain blood flow in their coronary arteries.
“I do not suggest that all people should wear face masks or do nothing outdoors,” Dr. Brook says. Still, he adds, perhaps those at highest risk – people with heart and lung diseases, obesity or diabetes – should attempt to reduce exposure.
Dr. Brauer and Oudyk agree that respirators present challenges. Even the relatively lightweight N95 will increase discomfort, Dr. Brauer says. Oudyk adds that high air pollution days often coincide with sweltering temperatures.
A healthy lifestyle may be the best defence for limiting the effects of air pollution, Dr. Brauer suggests. Addressing other cardiovascular disease factors like diet, fitness, stress, smoking and alcohol consumption will help reduce air pollution’s impact. “That’s probably more effective than anything you can do on the exposure side,” he says.
Ross notes that “the hierarchy of controls – hazard elimination, engineering controls, administrative controls and, finally, personal protective equipment – are difficult to apply to general air pollution.”
Dr. Allison Goldfine, head of clinic research at Boston’s Joslin Diabetes Center and a co-author of the PM2.5 study, notes in a statement that “while a lot of attention has correctly been attributed to caloric excess and sedentary behaviours, additional factors may provide novel approaches to diabetes prevention.”
Pearson says the evidence indicates that “current limits on particulate matter exposure may not adequately mitigate the public health consequences.” The challenge, he argues, is “much more of a societal issue and government policy issue of reducing exposure.”
Dan Birch is assistant editor of OHS CANADA.
John Oudyk discovered first-hand the significant amount of air pollution experienced by commuters.
One day, the registered occupational hygienist at the Occupational Health Clinics for Ontario Workers Inc.’s office in Hamilton, Ontario, was taking a city bus to a workplace to perform air quality testing. Travelling on the five-lane road downtown, Oudyk flipped on his air quality monitor.
“I was shocked at the amount of carbon monoxide, for instance, that I was picking up just sitting on the bus,” he says. “I don’t think we realize how much traffic air pollution [commuters are] exposed to, especially in the summer when we’ve got all the windows down.”
John Pearson, a researcher with Children’s Hospital Boston, says that a person stuck in highway traffic while commuting is “getting a lot higher pollution exposure than you are if you’re just walking around the city.”
In a study, Pearson writes that although environmental regulations in the United States have resulted in reduced exposure to PM2.5 (particulate matter between 0.1 and 2.5 microns in size), it may be a neglected risk factor for diabetes. Commuting “may contribute to chronic disease through increased pollutant exposure, in addition to increased sedentary time and reduced time for physical activity.”