February 15, 2012

The top sources of air pollution are burning fossil fuels (such as gas, oil, and coal), and industrial emissions, both of which are prevalent in the Salt Lake Valley, a smog-rich environment. Fine particulate matter pollutants consist of microscopic particles of metal, carbon, sulfates, and other materials that result from these sources of pollution. These specks of dust are about 30 times smaller than the thickness of a human hair, so they can be inhaled deep into the lungs. Breathing fine particulate matter may harm the cardiovascular system in two ways: if particles find their way into the bloodstream they can make blood vessels less elastic, and they may also boost activity of the sympathetic nervous system, which tends to increase heart rate and blood pressure and trigger the release of stress hormones. New research suggests that even a brief uptick in traffic-related air pollution may be enough to increase a person's short-term risk of stroke. The study, published in the Archives of Internal Medicine, was conducted by researchers at Brown University School of Medicine, Beth Israel Deaconess Medical Center, and the Harvard School of Public Health. It analysed 10 years of data from a Boston stroke center. It found that strokes are more likely to occur immediately following 24-hour periods in which air quality drops from the range the Environmental Protection Agency considers “good” into "moderate." The study compared 1,705 stroke cases in the Boston area with detailed data on the day-to-day levels of various airborne pollutants, including vehicle emissions such as particulate matter, black carbon, and nitrogen dioxide. After taking into account each patient's medical history, the researchers concluded the odds of having a stroke were 34% higher following a day of "moderate" air quality than following a "good" air day. Based on this finding, they estimate that a 20% reduction of levels of fine particulate matter would have prevented 6,100 of the 184,000 stroke hospitalizations that occurred in the northeastern United States in 2007. A second study, appearing in the Journal of the American Medical Association, provides additional evidence that air pollution may increase cardiovascular risk. In that study, a team of French researchers at at the University Paris Descartes re-analyzed data from 34 previous studies conducted around the world. Most of the studies used methods similar to those analyzed by the Brown study. Higher levels of airborne pollutants, including particulate matter, carbon monoxide, nitrogen dioxide, and sulfur dioxide, were associated with a slight increase in the short-term risk of heart attack. The researchers observed an uptick in heart risk even at pollution levels classified as safe by the World Health Organization. The increase in heart attack risk was small on the individual level, but it can have a substantial impact at the population level. In addition to affecting blood flow, air pollution appears to increase inflammation, an immune system response that is believed to contribute to both heart disease and strokes. If inhaled pollutants reach the alveoli, the tiny sacs in the lungs where oxygen and carbon dioxide pass into and out of the bloodstream, they trigger an inflammatory reaction. They can also spread through the blood stream and reach the heart. Breathe!