OSLO (Reuters) - Harmful levels of road traffic noise affect one in four people in Europe and raise health risks ranging from sleepless nights to heart disease, the European Environment Agency said on Friday.

In a first EEA assessment of the impact of noise pollution in Europe, it said the din undermines the ability of children to concentrate in some schools and disrupts nature, for instance by drowning out the songs birds use to attract mates.

"Noise pollution is a major environmental health problem in Europe," the EEA report said, adding that what it called the "European soundscape" is under threat.

The Copenhagen-based EEA, a European Union agency, said traffic was the main source of noise above legal guidelines and affected around 125 million people, a quarter of the EU population. Railways, airports and industrial sites added to the cacophony.

The EEA estimated that environmental noise caused up to 10,000 premature deaths in Europe every year. More than 900,000 cases of hypertension could be traced to noise, which it said raises risks of insomnia and heart disease.

While many people did not report problems, almost 20 million adults felt "annoyance" at noise pollution and another eight million suffered disturbed sleep, the EEA said.

The World Health Organization also says that noise is an under-estimated threat.

The EEA findings indicated that Luxembourg, Bulgaria and Belgium had urban areas with the highest percentages of people exposed to high road noise levels while Malta, Iceland and Germany were the quietest.

The report called for better planning ranging from preserving quiet areas in cities to less noisy tyres on cars.

In another report in 2011, the European Commission reckoned that noise from road and rail traffic cost 40 billion euros ($49 billion) a year in terms of depressed prices for property beside noisy roads, medical bills and lower productivity at work.

(Reporting by Alister Doyle; Editing by Mark Heinrich)