Air pollution triggers around the same amount of heart attacks as individual risk factors such as physical exertion, alcohol, and coffee.
Anger, positive emotions, sexual activity, cocaine or marijuana use and respiratory infections can also trigger heart attacks to different extents. These findings appear in an Article Online First and in this week’s Lancet, written by Dr Tim S Nawrot, Hasselt University, Diepenbeek, Belgium and Catholic University of Leuven, Belgium, and colleagues from both institutions.
The authors combined data from 36 separate studies with a mean participant age ranging from 44 years for cocaine and marijuana use to 72 years for respiratory infection studies. The authors calculated the relative risk posed by each trigger, and the population-attributable fraction (PAF) of each, meaning the proportion of total heart attacks estimated to have been caused by that trigger.
Air pollution increased the risk of triggering a heart attack by 5%, while cocaine increased the risk by 23 times. Coffee increased the risk by 1.5 times and alcohol by 3 times. However, since the entire population is exposed to air pollution, and only a tiny fraction (0.02%) is exposed to cocaine, air pollution triggers many more heart attacks than cocaine. The highest PAF was estimated for traffic exposure (time on the road/public transport) (7•4%), followed by physical exertion (6•2%), alcohol (5•0%), coffee (5•0%), air pollution defined by increased heavy particles in the air (4•8%), negative emotions (3•9%), anger (3•1%), heavy meal (2•7%), positive emotions (2•4%), sexual activity (2•2%), cocaine use (0•9%), marijuana smoking (0•8%) and respiratory infections (0•6%).
The authors say: “Of the triggers for heart attack studied, cocaine is the most likely to trigger an event in an individual, but traffic has the greatest population effect as more people are exposed to the trigger…PAFs give a measure of how much disease would be avoided if the risk was no longer present.”
While passive smoking was not included in the study, the authors note the mechanics of its effects are likely to be similar to that of outdoor air pollution, and there is additionally the evidence that bans on smoking in public places have reduced heart attack rates by 17%.
The authors note that substantial decreases in air pollution will be required in most cities to meet WHO standards for protecting public health. They conclude: “Our work shows that ever-present small risks might have considerable public health relevance…Improvement of the air we breathe is a very relevant target to reduce the incidence of this disease in the general population.”
In a linked Comment, Dr Andrea Baccarelli, Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA, and Dr Emelia J Benjamin, Cardiology and Preventive Medicine Sections, School of Medicine, Boston University, Boston, MA, USA, conclude: “Nawrot and colleagues have provided us with an exemplary piece of epidemiological work that furthers our understanding of myocardial infarction triggers. Their 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.”
Original Press release by Eureka Alert
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