As any city cyclist will know, riding your bike in heavy traffic can be, metaphorically speaking, a heartstopping experience.

But now research has found that it is literally one of the biggest triggers of heart attacks.

In a new sliding scale of everyday risks that prove the “final straw” in bringing on a heart attack, spending time in traffic - as a driver, cyclist or commuter - tops the list because of factors including stress and exposure to pollution.

But of these, cyclists are in greatest danger because they are more heavily exposed to pollution and are subjecting themselves to another major heart attack trigger, exercise.

The study, which analysed 36 pieces of research, is the first time the “final straw” risk factors for triggering heart attacks - rather than underlying causes of heart disease - have been quantified. While some factors overlap, they were ranked by scientists in The Lancet medical journal online, after the proportion of total heart attacks caused by different triggers was calculated.

Traffic exposure was blamed for 7.4 percent of heart attacks, followed by physical exertion with 6.2 percent.

Overall air pollution triggered between 5 percent and 7 percent of heart attacks, while drinking alcohol or coffee accounted for 5 percent.

Other risk factors included negative emotions (3.9 percent), anger (3.1 percent), eating a heavy meal (2.7 percent), positive emotions (2.4 percent) and sexual activity (2.2 percent). Cocaine was to blame for 0.9 percent of heart attacks, but this was because of limited exposure to the drug among the population.

On an individual basis, taking cocaine was shown to raise a person’s risk of having a heart attack 23-fold, according to the study, led by Dr Tim Nawrot, from Hasselt University in Belgium.

In comparison, air pollution led to a 5 percent extra risk, but since far more people are exposed to traffic fumes and factory emissions than cocaine, air quality is a far more important population-wide threat.

Professor David Spiegelhalter, a risk expert from Cambridge University, said it was difficult to “disentangle” the risk factors in the study for certain situations, such as driving or cycling to work in heavy traffic.

“A lot of other factors are contributing to the overall risk; air pollution, stress, physical exertion, even anger which is another well-known trigger for a heart attack. It’s a complex mix,” he added.

Judy O’Sullivan, senior cardiac nurse at the British Heart Foundation, said the benefits of exercising outdoors outweighed the risks from air pollution for most individuals, and urged people not to be put off running, walking or cycling in towns and cities.

Dr Tim Chico, honorary consultant cardiologist at the University of Sheffield, said: “We know a lot about why people suffer heart attacks (for example smoking, high cholesterol, obesity) but not much about why they occur on a particular day and time.”

But he stressed: “The foundations of heart disease are laid down over many years.

“If someone wants to avoid a heart attack they should focus on not smoking, exercising, eating a healthy diet and maintaining their ideal weight.” - Daily Mail