Living near a busy road is as likely to cause a fatal heart attack as being obese or a smoker, warns a new study.
Researchers suspect damaging air particles from traffic pollution could be behind the phenomenon.
A study of 107,130 women with an average age of 60 showed those whose homes were within 50 metres (164 feet) of a major road increased the risk by 38 percent compared to being at least 500 metres (0.3 miles) away.
Each 100 metres (328 feet) closer to roadways was associated with a six per cent rise in danger.
During the course of the study the risk of dying from coronary heart disease also rose by 24 per cent for those living near a busy road.
The Environmental Protection Agency estimated 35 million people in the US lived within 300 metres (984 feet) of a major road in 2009 - and a growing number lived in close proximity to major roads worldwide.
The public's exposure to major roadways is comparable to major sudden cardiac death risk factors, said researchers.
Previous research has found a modest increase in the risk of developing coronary heart disease among people who live near major roadways.
But the new study, published in the journal Circulation is believed to be the first to examine the impact of roadway proximity to the risk of a sudden heart attack.
Dr Jaime Hart, of Brigham and Women's Hospital in the United States, said: 'It's important for healthcare providers to recognise environmental exposures may be under-appreciated risk factors for diseases such as sudden cardiac death and fatal coronary heart disease.
'On a population level living near a major roadway was as important a risk factor as smoking, diet or obesity.'
The participants were part of the Nurses' Health Study from 1986 to 2012 and the researchers calculated the distance of their residences to roadways. They also took into account other factors including age, race, cigarette smoking, physical activity and diet.
During the study there were 523 cases of sudden cardiac death and 1,159 cases of fatal coronary heart disease. Researchers weren't able to measure all possible risk factors associated with living near a major road.
They also said more research is needed among men and among women of different ages, races and income levels because nearly all participants were middle-age to elderly, white and of middle- to upper-socioeconomic class.
Dr Hart said: 'Regardless of where you live adopting heart-healthy habits such as maintaining a healthy weight, being physically active, eating nutritious foods, quitting smoking and managing stress can help decrease your risk of heart and blood vessel disease.
'Our next step is to try to determine what specific exposures - such as air pollution - are driving the association between heart disease and major roadway proximity.'
