How earplugs can help your heart: health effects of noise pollution. (Science Selections).

Noise exposure can lead to small increases in blood pressure readings and possibly even increases in cardiovascular disease prevalence, conclude researchers from the National Institute of Public Health and the Environment in Bilthoven, the Netherlands, after filtering their way through more than 500 studies of health effects potentially linked with noise exposure [EHP 110:307-317]. But the limited number of health end points investigated and the lack of consistent methodologies have left large gaps in our knowledge of noise impacts, says lead researcher Elise E. M. M. van Kempen.

Noise is suspected of causing a number of adverse physiologic effects, ranging from hearing loss to myocardial infarction. Studies conducted to date suggest there is little risk of permanent hearing damage from noise below 70 decibels, which is the level typically found in a car or office setting. A jackhammer operates at about 100 decibels, and a jet taking off generates about 130 decibels. Other health end points studied have included elevated blood pressure, angina pectoris, ischemic heart disease, use of antihypertensive or cardiovascular drugs, and consultation with a doctor (for unspecified reasons).

Of the 500-plus studies the team reviewed, 43 contained data adequate for inclusion in a meta-analysis. The studies were conducted around the world from 1970 to 1999, covered a variety of occupational and community settings, and contained study populations ranging in size from 46 to 35,150. Studies in occupational settings tended to cover higher noise levels (up to 116 decibels) that were actually measured, while studies in community settings tended to cover lower levels (up to 80 decibels) that were estimated, not measured.

Based on results from nine pertinent studies, the team found a small but significant link between occupational noise exposure and hypertension. Exposure to air traffic noise in community settings also showed a small but significant link with hypertension, but only one study covered that scenario. A few other studies in community settings showed statistically insignificant links between road traffic noise exposure and myocardial infarction and ischemic heart disease, and between air traffic noise exposure and angina pectoris, the use of cardiovascular drugs, and consultation with a doctor.

To gain a better understanding of potential health effects from exposure to higher noise levels, which tens of millions of people routinely encounter, van Kempen and her colleagues recommend that researchers undertake additional studies that address the many shortcomings identified in existing studies. For instance, most studies did not investigate confounding factors such as an individual's weight or smoking and alcohol consumption habits. Nor did researchers look at other pollutants associated with particular occupational and community settings. Noise levels often were simply estimated or, if measured, did not necessarily reflect the exposure of a particular individual, but rather that of the immediate area around the noise detector. Blood pressure measurements often were based on just one reading. Long-term health effects were poorly evaluated. And studies that were conducted but not published, which the team concludes has been a likely occurrence, skew the data base by reducing its size and altering the weight given to certain findings. For instance, the team concludes that studies that found a relatively small effect from noise exposure have been published less often than might be expected.