Noise Pollution Takes Toll on Health and Happiness

A now-classic study conducted in the 1970s was among the first to indicate that such noise is more than an annoyance. It found that children living on the lower, noisier floors of an apartment building overlooking a busy Manhattan bridge had lower reading scores than those living on higher floors.

But was noise really the major factor explaining that difference? After all, people tend to move away from extremely noisy neighborhoods if they can, and those who don't are more likely to be poor, which by itself is a risk factor for delayed educational advancement and ill health.

To answer such questions, scientists have taken advantage of unusual situations in which people's exposure to noise changed over time while other factors remained relatively constant. In a study of students attending an elementary school near noisy train tracks in New York, for example, researchers showed that by the time the students reached sixth grade, those whose classrooms faced the train were a year behind those whose classrooms were on the quiet side of the building. After noise reduction materials were installed in the classrooms and around the tracks, reading scores in the two groups equalized, strengthening the case that noise was the culprit.

Another clue came from a study of children whose schools were located near West London's busy Heathrow airport.

"We found a straightforward linear effect from aircraft noise and impairment in reading on standardized tests," said study leader Stephen A. Stansfeld, a professor of psychiatry at Queen Mary's School of Medicine and Dentistry in London, noting that the close correlation strengthened the case that noise was to blame.

But it was a "natural" experiment in Germany that helped clinch the case, when the old Munich airport was shut down and a new one was opened at a distant site. Tests done on third- and fourth-graders -- before that switch, soon after it and again later on -- showed that students near the old airport initially scored lower than others on tests of memory and reading but improved after the airport closed, while their counterparts living near the new airport saw a decline in scores after the switch occurred.

A Chronic Emergency

Noise that invades a classroom may make it hard for students to hear the teacher, of course. But blood tests done on the Munich children helped reveal a more insidious biological mechanism through which noise wreaks much of its havoc. Children near the working airports had significantly higher levels of adrenaline and cortisol -- the body's so-called stress hormones.

Those hormones are part of the body's "fight or flight" response, which helps a person deal with sudden emergencies. Blood pressure and heart rate go up in preparation for action. The blood becomes thick with oxygen-toting red blood cells. And the immune system gets suppressed as part of the shift toward fulfilling short-term needs rather than longer-term health.

That response can be lifesaving in an attack, but it is counterproductive when activated chronically. Over months and years it can literally corrode the body, eating away at blood vessels and other organs and predisposing a person to other medical woes.

"This is the most disturbing thing about noise, because it means you are being exposed to this reaction all the time," said Roberto Bertollini of the World Health Organization's Special Programme on Health and Environment.

As a result of that hormonal activation, children near the working Munich airports had significantly higher blood pressure than children in quieter neighborhoods -- adding to their risk of having a heart attack or stroke later in life. Similar impacts have been documented among adults near Amsterdam's Schiphol airport and Stockholm's Arlanda airport, where chronic noise as low as 55 decibels correlated with more doctor visits, high blood pressure and treatments for heart troubles.

Whether traffic noise actually increases one's chances of having heart disease or a heart attack has been harder to determine, because such studies require large numbers of people. But the evidence for at least a modest effect is growing.