A small increase in toxic fumes enhances the risk by at least 20 percent but this rises to 72 percent in smokers.

       Lead author Dr Youn-Hee Lim, of Copenhagen University, said: "We found long-term exposure to specific air pollutants and road traffic noise increased the risk of incident heart failure, especially for former smokers or people with hypertension (high blood pressure), so preventive and educational measures are necessary.

       "Strategies like smoking cessation and blood pressure control must be encouraged."

       The study involved 22,000 Danish female nurses aged 44 or over who were recruited in the 1990s and tracked for up to 20 years.

       Data was collected on levels of fine particulate matter (PM2.5s) and nitrogen dioxide (NO2) from cars, trucks and buses around their homes and findings were analysed.

       Road traffic noise was measured in decibels (dBs). For every 5.1 and 8.6mcg/m3 (micrograms per cubic metre) increase in PM2.5s and NO2 over three years, the risk of heart failure rose by 17 and 10 percent respectively.

       For every 9.3dB increase in road traffic noise, the risk rose on average by 12 percent.

       Dr Lim said: "We were surprised by how two environmental factors interacted.

       "Air pollution was a stronger contributor to heart failure incidence compared to road traffic noise but the women exposed to both high levels of air pollution and road traffic noise showed the highest increase in heart failure risk.

       "However, 30 percent of the nurses with heart failure had a previous history of hypertension, and they were the most susceptible population to air pollution exposure."

       Air pollution causes around 50,000 deaths a year in the UK, mostly from circulatory conditions, while heart failure affects 900,000 people.

       The study is published in the Journal of the American Heart Association.

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