We all know that high cholesterol, obesity and high blood pressure can increase the risk of having a heart attack. On the behavioral side, triggers include getting angry, exerting yourself and feeling stressed. But none of these individual risk factors account for as many heart attacks as population-level influences like the quality of the air we breathe, a new review study finds.
To calculate how population-wide environmental factors stack up against more individual risks for heart attacks, researchers in Belgium and Switzerland extrapolated data from 36 studies that analyzed various triggers, including caffeine, physical exertion, heavy meals, anger and even cocaine use. The study authors then came up with a rough ranking of which factors contributed the most to heart attacks in a population. (More on Time.com: Diet Soda May Lead to Stroke Risk? Really?)
Exposure to traffic, which can increase blood pressure as well as absorption of heart-harming exhaust, seemed to pose the greatest relative risk to the heart, accounting in the researchers’ model for 7.4% of attacks. This was followed by physical exertion, responsible for about 6% of heart attacks, and then by alcohol, coffee and air pollution, each of which contributed to about 5% of events. (Other smaller risks included anger, sex and smoking marijuana.)
The scientists measured air pollution as a change in particulate matter of 30 micrograms (mcg) per cubic meter of air or more. The World Health Organization recommends a mean concentration of about 20 mcg of particulates per cubic meter of air, and that’s where concentrations in most major U.S. cities stand, making a decrease of 30 mcg/cubic meter, as recommended in the study, impractical. However, even a drop in pollution of 10 mcg/cubic meter, the researchers found, could account for up to a 2% decrease in heart attacks, making that perhaps a more realistic goal. That’s in line with previous studies that suggested with every 10 mcg/cubic meter increase in particulates, the risk of a heart-related death goes up by 1.4%.
As Andrea Baccarelli and Emilia Benjamin of the Harvard School of Public Health wrote in a commentary accompanying the Lancet study:
[This] work stands as a warning against overlooking the public health relevance of risk factors with moderate or weak strength that have high frequency in the community.
What that means is that some “weak” community risk factors may be more important to the overall heart health of a population than stronger individual factors. For instance, cocaine use was rated as among the strongest contributors for individuals in causing a heart attack — the drug accounted for nearly a 24-fold increase in risk among users compared to nonusers. But because the proportion of any given population that abuses cocaine is relatively small, the overall increase of a community’s heart attack risk due to cocaine is just under 1%. (More on Time.com: Post–Super Bowl Heartbreak: Cardiac Death Risk May Rise for Losing Fans)
As study co-author Tim Nawrot of the Center for Environmental Sciences at Hasselt University told WebMD:
The relevance of air pollution as a trigger in the population is of the same magnitude of risk of many other clinically appreciated or recognized triggers for [heart attack].
The study raises interesting questions about widening the focus on heart attack triggers — away from a narrow consideration of individual risk factors, which are certainly important, to include more universal ones, such as air quality or traffic exposure, which are ubiquitous problems in cities.