The researchers evaluated several kinds of fine particles found in urban air pollution. These included sulfate particles, which come mainly from coal-burning power plants, as well as ultra-fine particles and black carbon soot, which are generated primarily by diesel- and gasoline-powered vehicles.
"Our strongest finding was that blood vessel reactivity was impaired in people with diabetes on days when concentrations of sulfate particles and black carbon were higher," said Marie O'Neill, Ph.D., an epidemiologist now with the Robert Wood Johnson Health & Society Scholars program at University of Michigan and lead author on the study. "Impaired vascular reactivity has been associated with an increased risk of heart attack, stroke and other heart problems."
"Previous studies have shown that when air pollution levels are higher, people with diabetes have higher rates of hospitalization and death related to cardiovascular problems," said NIEHS Director David Schwartz, M.D. "These changes in blood vessel reactivity may help explain this phenomenon."
The National Institute of Environmental Health Sciences, one of the National Institutes of Health, provided funding to O'Neill and other researchers at the Harvard School of Public Health for the study. Other collaborators were from the Joslin Diabetes Center and Beth Israel Deaconess Medical Center in Boston. The findings are published in the June 2005 issue of the journal Circulation.
"We don't really understand why fine particles may cause this decrease in vascular reactivity," said O'Neill. "Further research is needed to confirm this association between air pollution and vascular health and to understand what causes people with diabetes to be especially sensitive."
Researchers recruited 270 greater Boston metropolitan residents and divided them into two groups. The first group consisted of subjects with a positive diagnosis of type I or type II diabetes. The second group included subjects who were not diabetic, but who had a family history of diabetes or blood sugar levels slightly higher than normal.
The investigators used a technique called brachial artery ultrasound to assess blood vessel response in the study subjects. The measurement was obtained by applying a pressure cuff to the subject's upper arm and cutting off the blood flow through the arm's main artery. Researchers then released the cuff, allowing the blood to rush through. The researchers then evaluated changes in the diameter of the main artery as a result of the physical stress placed on the vessel.
"We observed an 11 percent decrease in diabetics' vascular reactivity on days when sulfate particle concentrations were higher than normal," said O'Neill. "We also noted a 13 percent decrease in their vascular reactivity on days with higher-than-normal black carbon concentrations."
"We hope our study will remind people that reducing air pollution is important for everyone's health, but especially for vulnerable members of our population, including the elderly and people with chronic health problems such as diabetes," she said.
Diabetes is a metabolic disorder in which blood sugar levels are elevated because levels of insulin are too low. Insulin is the hormone needed to process sugars and starches into energy. Diabetes is widely recognized as one of the leading causes of death and disability in the United States, affecting some 13.3 million Americans. Research conducted in Montreal, Quebec from 1984 to 1993 showed that hospitalizations and deaths related to cardiovascular problems increased among diabetics when levels of air pollution were higher.
The funding for the air pollution monitoring was provided by the Environmental Protection Agency's Particulate Matter Research Center.