Exposure to high levels of aircraft noise near busy international airports has been linked to a higher risk of heart disease and strokes in two separate studies from Britain and the United States.Researchers in London studied noise and hospital admissions around London Heathrow Airport, while a separate team analysed data on six million Americans living near 89 US airports.Both studies, published in the British Medical Journal on Wednesday, found that people living with the highest levels of aircraft noise had increased risks of stroke, coronary heart disease and other cardiovascular diseases.In the Heathrow study, the risks were around 10 to 20 per cent higher in areas with highest levels of aircraft noise, compared with the areas with least noise.Stephen Stansfeld, a professor at Queen Mary University of London, who was not part of either research team but provided a commentary on their findings, said the results suggested that "aircraft noise exposure is not just a cause of annoyance, sleep disturbance, and reduced quality of life” but may also increase sickness and death from heart disease.City and town planners "need to take this into account when extending airports in heavily populated areas or planning new airports,” he said.Other experts said the studies raised important issues about aircraft noise and health but did not establish a causal link."Both of these studies are thorough and well conducted. But, even taken together, they don’t prove that aircraft noise actually causes heart disease and strokes,” said Kevin McConway, a professor of applied statistics at Britain’s Open University.The British research team set out to investigate the risks of stroke and heart disease in relation to aircraft noise among 3.6 million people living near Heathrow, one of the busiest airports in the world.They compared hospital admissions and death rates due to stroke and heart disease from 2001 to 2005 in 12 areas of London and nine further districts to the west of London.Levels of aircraft noise for each area were obtained from the Civil Aviation Authority (CAA), and factors that could have affected the results, such as age, sex, ethnicity, social deprivation, smoking, air pollution and road traffic noise were also taken into account.Their results showed increased risks of stroke, coronary heart disease, and cardiovascular disease, especially among the 2 per cent of the study population exposed to the highest levels of daytime and night time aircraft noise."The exact role that noise exposure may play in ill health is not well established,” said Anna Hansell of Imperial College London, who led the British study. "However, it is plausible that it might be contributing, for example by raising blood pressure or by disturbing people’s sleep.”The researchers noted that discussions on possible expansion plans for London’s airport capacity have been on and off the table for many decades, with demand for air travel expected to double in Britain to 300 million passengers per year by 2030.In a second study also published in the the British Medical Journal , researchers at the Harvard School of Public Health and Boston University School of Public Health looked at data for more than six million Americans aged 65 or over living near 89 US airports in 2009.The research, the first to analyse a large population across numerous airports, found that, on average, zip codes with 10-decibel (dB) higher aircraft noise had a cardiovascular hospital admission rate that was 3.5 per cent higher.The results showed that people exposed to the highest noise levels — more than 55 dB — had the strongest link with hospitalisations for heart disease, and the link also remained after adjustment for socio-economic status, demographic factors, air pollution, and proximity to roads.Conway said because of the kind of data used, the studies could only "suggest very strongly that we should find out much more about aircraft noise and circulatory disease.”